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>
    <alllinks galcontinue="En:Wikipedia:Collapsible_tables|456" />
  </query-continue>
  <query>
    <pages>
      <page pageid="279" ns="0" title="計画一覧" />
      <page pageid="340" ns="0" title="BTミサイル発射" />
      <page pageid="462" ns="10" title="テンプレート:Main" />
      <page pageid="472" ns="10" title="テンプレート:See also" />
      <page pageid="498" ns="0" title="BTミサイル" />
      <page pageid="508" ns="0" title="核ミサイル" />
      <page pageid="566" ns="0" title="汚染土壌" />
      <page pageid="858" ns="0" title="お座敷箱庭" />
    </pages>
  </query>
</api>