Apex domains cannot have CNAME records.
Question and response
Question
dig smktg.jp. NS
Answer
smktg.jp. 5 NS ns-831.awsdns-39.net.
smktg.jp. 5 NS ns-1344.awsdns-40.org.
smktg.jp. 5 NS ns-2031.awsdns-61.co.uk.
smktg.jp. 5 NS ns-409.awsdns-51.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0