Apex domains cannot have CNAME records.
Question and response
Question
dig cloud-isle.jp. NS
Answer
cloud-isle.jp. 5 NS ns-786.awsdns-34.net.
cloud-isle.jp. 5 NS ns-122.awsdns-15.com.
cloud-isle.jp. 5 NS ns-1665.awsdns-16.co.uk.
cloud-isle.jp. 5 NS ns-1312.awsdns-36.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0