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>
    <alltransclusions>
      <t ns="10" title="テンプレート:Navi cele11" />
      <t ns="10" title="テンプレート:Navi cele12" />
      <t ns="10" title="テンプレート:Navi cele13" />
      <t ns="10" title="テンプレート:Navi cele14" />
      <t ns="10" title="テンプレート:Navi celex" />
      <t ns="10" title="テンプレート:Socialbutton" />
    </alltransclusions>
  </query>
</api>