diff --git a/CHANGES.md b/CHANGES.md
index 6c77b06..435c4a2 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -9,7 +9,12 @@ To be released.
  -  Since this version, it requires GHC 8.8.* at least, and supports GHC 9.0.*
     at most.
 
- -  Now supports several content types besides HTML/XHTML.  [[#18]]
+ -  Now supports several content types besides HTML/XHTML.  The below list
+    shows all supported content types:  [[#18]]
+
+     -  `text/html` (previously non-XHTML mode)
+     -  `application/xhtml+xml` (previously XHTML mode)
+     -  `text/plain` (added)
 
     The below Haskell APIs changed:
 
diff --git a/demo/src/Demo.elm b/demo/src/Demo.elm
index 8872bdb..9cd949c 100644
--- a/demo/src/Demo.elm
+++ b/demo/src/Demo.elm
@@ -118,6 +118,7 @@ type alias Source =
 type ContentType
     = Html
     | Xhtml
+    | PlainText
 
 
 type Options
@@ -250,6 +251,9 @@ makeInput source =
 
                         Xhtml ->
                             "appplication/xhtml+xml"
+
+                        PlainText ->
+                            "text/plain"
               )
             ]
         <|
@@ -1325,15 +1329,22 @@ viewOptions model =
                                         Xhtml
 
                                     _ ->
-                                        Html
+                                        PlainText
                     ]
                   <|
                     [ Select.item
                         [ value "text/html", selected <| contentType == Html ]
                         [ text "HTML" ]
                     , Select.item
-                        [ value "application/xhtml+xml", selected <| contentType == Xhtml ]
+                        [ value "application/xhtml+xml"
+                        , selected <| contentType == Xhtml
+                        ]
                         [ text "XHTML" ]
+                    , Select.item
+                        [ value "text/plain"
+                        , selected <| contentType == PlainText
+                        ]
+                        [ text "Plain text" ]
                     ]
                 ]
             ]
diff --git a/package.yaml b/package.yaml
index ea5e007..35f877f 100644
--- a/package.yaml
+++ b/package.yaml
@@ -73,6 +73,7 @@ library:
   - data-default >= 0.2 && < 1
   - filepath >= 1 && < 2
   - file-embed >= 0.0.10 && < 0.0.16
+  - html-entities >= 1 && < 2
   when:
   - condition: flag(static) || flag(embed-dictionary)
     then:
diff --git a/scripts/deno/mod.ts b/scripts/deno/mod.ts
index 2e3f280..679f46d 100644
--- a/scripts/deno/mod.ts
+++ b/scripts/deno/mod.ts
@@ -35,13 +35,18 @@ export interface Preset {
  */
 export type Dictionary = "kr-stdict";
 
+export type ContentType =
+  | "text/html"
+  | "application/xhtml+xml"
+  | "plain/text";
+
 /**
  * Options for transformation.
  * See also <https://github.com/dahlia/seonbi#http-api>.
  */
 export interface Options {
   /** Content type. */
-  contentType: "text/html" | "application/xhtml+xml";
+  contentType: ContentType;
   /** Quoting options. */
   quote:
     | "CurvedQuotes"
diff --git a/src/Text/Seonbi/ContentTypes.hs b/src/Text/Seonbi/ContentTypes.hs
index e684a17..8b292d3 100644
--- a/src/Text/Seonbi/ContentTypes.hs
+++ b/src/Text/Seonbi/ContentTypes.hs
@@ -7,6 +7,7 @@ module Text.Seonbi.ContentTypes
     , TextTransformer
     , asHtmlTransformer
     , asHtmlTransformer'
+    , asPlainTextTransformer
     , asXhtmlTransformer
     , contentTypeFromText
     , contentTypes
@@ -25,8 +26,11 @@ import Data.CaseInsensitive
 import Data.Set
 import Data.Text as ST
 import Data.Text.Lazy as LT
+import Data.Text.Lazy.Builder
+import HTMLEntities.Decoder
 
 import Text.Seonbi.Html
+import qualified Text.Seonbi.Html.TagStack as TagStack
 
 -- | Represents a function that transforms an 'HtmlEntity' list.
 type HtmlTransformer m
@@ -73,6 +77,18 @@ asHtmlTransformer = asHtmlTransformer' False
 asXhtmlTransformer :: (Monad m, MonadFail m) => TransformerTransformer m
 asXhtmlTransformer = asHtmlTransformer' True
 
+asPlainTextTransformer :: (Monad m, MonadFail m) => TransformerTransformer m
+asPlainTextTransformer transformer text' = do
+    let entities = [HtmlCdata TagStack.empty $ LT.toStrict text']
+    output <- transformer entities
+    return . LT.concat $
+        [ case e of
+            HtmlCdata _ cdata -> LT.fromStrict cdata
+            HtmlText _ rawText' -> toLazyText $ htmlEncodedText rawText'
+            _ -> LT.empty
+        | e <- output
+        ]
+
 -- | Represents a case-insensitive content type.
 type ContentType = CI ST.Text
 
@@ -91,6 +107,7 @@ transformers :: (Monad m, MonadFail m)
 transformers =
     [ ("text/html", TransformerTransformer' asHtmlTransformer)
     , ("application/xhtml+xml", TransformerTransformer' asXhtmlTransformer)
+    , ("text/plain", TransformerTransformer' asPlainTextTransformer)
     ]
 
 -- | Supported content types.
diff --git a/test/Text/Seonbi/ContentTypesSpec.hs b/test/Text/Seonbi/ContentTypesSpec.hs
index f42a684..1c514aa 100644
--- a/test/Text/Seonbi/ContentTypesSpec.hs
+++ b/test/Text/Seonbi/ContentTypesSpec.hs
@@ -25,10 +25,15 @@ spec = do
     specify "asXhtmlTransformer" $ do
         r <- asXhtmlTransformer textReverser "<p>foo <em>bar</em><br> baz</p>"
         r `shouldBe` "<p> oof<em>rab</em><br/>zab </p>"
+    specify "asPlainTextTransformer" $ do
+        r <- asPlainTextTransformer textReverser
+                "<p>foo <em>bar</em><br> baz</p>"
+        r `shouldBe` ">p/<zab >rb<>me/<rab>me< oof>p<"
     specify "transformWithContentType" $ do
         let input = "<p>foo <em>bar</em><br></p>"
         h <- transformWithContentType "text/html" textReverser input
         h `shouldBe` "<p> oof<em>rab</em><br></p>"
         x <- transformWithContentType "application/xhtml+xml" textReverser input
         x `shouldBe` "<p> oof<em>rab</em><br/></p>"
-
+        p <- transformWithContentType "text/plain" textReverser input
+        p `shouldBe` ">p/<>rb<>me/<rab>me< oof>p<"