Apex domains cannot have CNAME records.
Question and response
Question
dig sls.jpne.co.jp. NS
Answer
sls.jpne.co.jp. 4 NS ns-1747.awsdns-26.co.uk.
sls.jpne.co.jp. 4 NS ns-379.awsdns-47.com.
sls.jpne.co.jp. 4 NS ns-734.awsdns-27.net.
sls.jpne.co.jp. 4 NS ns-1189.awsdns-20.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0