ns2.web.ad.jp has no CNAME records.
Question and response
Question
dig ns2.web.ad.jp. NS
Answer
The response has no answer records.
Authority
web.ad.jp. 77 SOA ns.center.web.ad.jp. ns-admin.web.ad.jp. 671 10800 1800 3600000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0