Apex domains cannot have CNAME records.
Question and response
Question
dig secom-cloud.jp. NS
Answer
secom-cloud.jp. 5 NS a3-64.akam.net.
secom-cloud.jp. 5 NS a26-64.akam.net.
secom-cloud.jp. 5 NS a13-64.akam.net.
secom-cloud.jp. 5 NS a14-66.akam.net.
secom-cloud.jp. 5 NS a1-129.akam.net.
secom-cloud.jp. 5 NS a28-66.akam.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0