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>
    <allpages gapcontinue="一般固有値" />
  </query-continue>
  <query>
    <pages>
      <page pageid="2" ns="0" title="Windows Tips" contentmodel="wikitext" pagelanguage="ja" touched="2015-03-02T15:26:07Z" lastrevid="26" counter="1421" length="263" />
      <page pageid="13" ns="0" title="Αβ型漸化式" contentmodel="wikitext" pagelanguage="ja" touched="2015-02-15T09:51:30Z" lastrevid="18" counter="914" length="1784" new="" />
      <page pageid="10" ns="0" title="プログラミング言語、処理系" contentmodel="wikitext" pagelanguage="ja" touched="2015-02-15T10:06:43Z" lastrevid="21" counter="1928" length="202" />
      <page pageid="1" ns="0" title="メインページ" contentmodel="wikitext" pagelanguage="ja" touched="2015-02-15T06:26:43Z" lastrevid="16" counter="6503" length="1521" />
    </pages>
  </query>
</api>