Apex domains cannot have CNAME records.
Question and response
Question
dig siterock.co.jp. NS
Answer
siterock.co.jp. 4 NS ttnet01.siterock.co.jp.
siterock.co.jp. 4 NS jens01.siterock.co.jp.
siterock.co.jp. 4 NS ns.spin.ad.jp.
siterock.co.jp. 4 NS ns.tokyo.spin.ad.jp.
Authority
The response has no authority records.
Additional
jens01.siterock.co.jp. 4 A 202.33.115.2
ttnet01.siterock.co.jp. 4 A 210.249.183.162
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0