diff --git a/README.md b/README.md
index 04f53a68..7d986ddb 100644
--- a/README.md
+++ b/README.md
@@ -65,7 +65,7 @@
 | 6.2.5 Syntax of numerical constants | yes | |
 | 6.2.6 Numerical operations | yes | some functions that return multiple values are not supported for now. Also, picrin does not provide complex library procedures. |
 | 6.2.7 Numerical input and output | no | |
-| 6.3 Booleans | incomplete | TODO: `boolean=?` |
+| 6.3 Booleans | yes | |
 | 6.4 Pairs and lists | yes | |
 | 6.5 Symbols | incomplete | TODO: `symbol=?`, `symbol->string`, `string->symbol` |
 | 6.6 Characters | incomplete | TODO: almost all functions in the section :-( |
diff --git a/piclib/built-in.scm b/piclib/built-in.scm
index 6a27bf5b..e98b043b 100644
--- a/piclib/built-in.scm
+++ b/piclib/built-in.scm
@@ -244,3 +244,13 @@
 	     (eq? '*values-tag* (car res)))
         (apply consumer (cdr res))
         (consumer res))))
+
+(define (boolean=? . objs)
+  (define (every pred list)
+    (if (null? list)
+	#t
+	(if (pred (car list))
+	    (every pred (cdr list))
+	    #f)))
+  (or (every (lambda (x) (eq? x #t)) objs)
+      (every (lambda (x) (eq? x #f)) objs)))