You are looking at the HTML representation of the XML format.
HTML is good for debugging, but is unsuitable for application use.
Specify the format parameter to change the output format.
To see the non HTML representation of the XML format, set format=xml.
See the complete documentation, or API help for more information. 
<?xml version="1.0"?>
<api>
  <query-continue>
    <allfileusages gafcontinue="BAD12357120.png|366" />
  </query-continue>
  <query>
    <pages>
      <page pageid="23" ns="0" title="印欧語における「神」の語源について" />
      <page pageid="68" ns="0" title="ヒエログリフ豆知識" />
      <page pageid="188" ns="0" title="Ｍ神列伝１：ヒエログリフ" />
      <page pageid="366" ns="0" title="地平線の太陽：ヒエログリフ" />
      <page pageid="440" ns="0" title="かき消されるＢ：ヒエログリフ" />
    </pages>
  </query>
</api>