Apex domains cannot have CNAME records.
Question and response
Question
dig ilb.jp-east-2.idcfcloud.net. NS
Answer
ilb.jp-east-2.idcfcloud.net. 3 NS ns01.idcfcloud.com.
ilb.jp-east-2.idcfcloud.net. 3 NS ns02.idcfcloud.com.
ilb.jp-east-2.idcfcloud.net. 3 NS ns03.idcfcloud.com.
Authority
The response has no authority records.
Additional
ns01.idcfcloud.com. 2 A 210.140.183.89
ns02.idcfcloud.com. 2 A 211.10.28.207
ns03.idcfcloud.com. 2 A 202.230.203.7
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0