Apex domains cannot have CNAME records.
Question and response
Question
dig wide.ad.jp. NS
Answer
wide.ad.jp. 2 NS ns.tokyo.wide.ad.jp.
wide.ad.jp. 2 NS mango.itojun.org.
wide.ad.jp. 2 NS ns-wide.wide.ad.jp.
Authority
The response has no authority records.
Additional
ns.tokyo.wide.ad.jp. 2 A 203.178.136.35
mango.itojun.org. 3 A 210.155.141.200
ns-wide.wide.ad.jp. 2 A 203.178.136.59
ns.tokyo.wide.ad.jp. 2 AAAA 2001:200:0:1:0:0:0:6
mango.itojun.org. 3 AAAA 2001:2f0:0:8800:0:0:1:1
mango.itojun.org. 3 AAAA 2001:2f0:0:8800:226:2dff:fe0b:4311
ns-wide.wide.ad.jp. 2 AAAA 2001:200:0:1:0:0:0:f
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0