Apex domains cannot have CNAME records.
Question and response
Question
dig spcmail.jp. NS
Answer
spcmail.jp. 5 NS ns-798.awsdns-35.net.
spcmail.jp. 5 NS ns-257.awsdns-32.com.
spcmail.jp. 5 NS ns-1906.awsdns-46.co.uk.
spcmail.jp. 5 NS ns-1404.awsdns-47.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0