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="UbuntuにAtomをインストールする" />
  </query-continue>
  <query>
    <pages>
      <page pageid="66" ns="0" title="Ubuntu 17.10のネットワークの設定" contentmodel="wikitext" pagelanguage="ja" touched="2018-03-27T10:29:52Z" lastrevid="166" counter="" length="2713" new="" />
      <page pageid="26" ns="0" title="UbuntuでCPUの動作クロックを調べる方法" contentmodel="wikitext" pagelanguage="ja" touched="2015-05-02T02:36:43Z" lastrevid="54" counter="" length="1926" new="" />
      <page pageid="61" ns="0" title="Ubuntuでchef-clientをローカルモードで利用する" contentmodel="wikitext" pagelanguage="ja" touched="2016-12-15T03:28:18Z" lastrevid="151" counter="" length="866" new="" />
      <page pageid="63" ns="0" title="Ubuntuで名前解決ができない" contentmodel="wikitext" pagelanguage="ja" touched="2017-10-29T03:32:15Z" lastrevid="159" counter="" length="3676" new="" />
    </pages>
  </query>
</api>