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>
    <alltransclusions gatcontinue="encode|10" />
  </query-continue>
  <query>
    <pages>
      <page pageid="1" ns="0" title="メインページ" />
      <page pageid="5" ns="0" title="Pythonでのエンコードとデコード" />
      <page pageid="6" ns="0" title="Pythonでrot13を扱う" />
      <page pageid="7" ns="0" title="Pythonでbase64を扱う" />
      <page pageid="8" ns="0" title="Pythonで16進数を扱う" />
      <page pageid="9" ns="0" title="Pythonで2進数を扱う" />
      <page pageid="20" ns="0" title="pychecker" />
      <page pageid="41" ns="0" title="Pythonのリスト型" />
      <page pageid="71" ns="0" title="Pythonの集合型" />
    </pages>
  </query>
</api>