Apex domains cannot have CNAME records.
Question and response
Question
dig sc24.jp. NS
Answer
sc24.jp. 5 NS ns21.sc24.jp.
sc24.jp. 5 NS ns11.sc24.jp.
Authority
The response has no authority records.
Additional
ns11.sc24.jp. 5 A 203.178.84.118
ns21.sc24.jp. 5 A 203.178.75.166
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0