diff --git a/dbl.js b/dbl.js
new file mode 100644
index 0000000..348b561
--- /dev/null
+++ b/dbl.js
@@ -0,0 +1,14 @@
+// 例: フォント二倍化
+function dblSize() {
+    var pElements = document.getElementsByTagName('p');
+    if (pElements.length == 0) {
+	alert('p要素はこの文書にありません。');
+    } else {
+	for (let i of pElements) {
+	    i.style.fontSize = '200%';
+	}
+    }
+}
+document.addEventListener("DOMContentLoaded", function(e) {
+    document.body.addEventListener("click", dblSize);
+});