Apex domains cannot have CNAME records.
Question and response
Question
dig maildealer.jp. NS
Answer
maildealer.jp. 5 NS ns-1672.awsdns-17.co.uk.
maildealer.jp. 5 NS ns-985.awsdns-59.net.
maildealer.jp. 5 NS ns-334.awsdns-41.com.
maildealer.jp. 5 NS ns-1448.awsdns-53.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0