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>
    <allredirects garcontinue="RELIONビルド時のエラー1|5613" />
  </query-continue>
  <query>
    <pages>
      <page pageid="3816" ns="0" title="Matrix3D" />
      <page pageid="5040" ns="0" title="PIONEのインストール" />
      <page pageid="5076" ns="0" title="マークダウン" />
      <page pageid="5208" ns="0" title="変数束縛" />
      <page pageid="5458" ns="0" title="EosOnLInux" />
      <page pageid="5509" ns="0" title="RELIONのLinuxへの導入" />
      <page pageid="5634" ns="0" title="Dockerでデータ分析環境を作る" />
      <page pageid="5641" ns="0" title="Gitコマンド" />
      <page pageid="5647" ns="0" title="STARファイル" />
      <page pageid="5837" ns="0" title="MacOS/anaconda3" />
    </pages>
  </query>
</api>