Apex domains cannot have CNAME records.
Question and response
Question
dig nttpc.co.jp. NS
Answer
nttpc.co.jp. 4 NS ns2.sphere.ad.jp.
nttpc.co.jp. 4 NS ns1.sphere.ad.jp.
Authority
The response has no authority records.
Additional
ns1.sphere.ad.jp. 4 A 202.239.113.19
ns2.sphere.ad.jp. 4 A 202.239.113.26
ns1.sphere.ad.jp. 4 AAAA 2001:2c0:11:3:0:0:0:a01
ns2.sphere.ad.jp. 4 AAAA 2001:2c0:11:1:0:0:0:a02
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0