Apex domains cannot have CNAME records.
Question and response
Question
dig cloudz.jp. NS
Answer
cloudz.jp. 5 NS ns015-v4ltcj370vpoamq8.v.d-53.jp.
cloudz.jp. 5 NS ns015-v4ltcj370vpoamq8.v.d-53.info.
cloudz.jp. 5 NS ns015-v4ltcj370vpoamq8.v.d-53.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0