Apex domains cannot have CNAME records.
Question and response
Question
dig isize.com. NS
Answer
isize.com. 3 NS v46ns1.x.recruit.co.jp.
isize.com. 3 NS v46ns3.x.recruit.co.jp.
isize.com. 3 NS v46ns2.x.recruit.co.jp.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0