Apex domains cannot have CNAME records.
Question and response
Question
dig bekknet.ad.jp. NS
Answer
bekknet.ad.jp. 5 NS dns02.bekknet.ad.jp.
bekknet.ad.jp. 5 NS dns01.bekknet.ad.jp.
Authority
The response has no authority records.
Additional
dns01.bekknet.ad.jp. 5 A 202.235.199.100
dns02.bekknet.ad.jp. 5 A 202.210.128.100
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0