Apex domains cannot have CNAME records.
Question and response
Question
dig obc.jp. NS
Answer
obc.jp. 5 NS ns-1308.awsdns-35.org.
obc.jp. 5 NS ns-487.awsdns-60.com.
obc.jp. 5 NS ns-993.awsdns-60.net.
obc.jp. 5 NS ns-1693.awsdns-19.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0