Apex domains cannot have CNAME records.
Question and response
Question
dig nuriwebsoft.co.kr. NS
Answer
nuriwebsoft.co.kr. 2 NS ns102.dnsever.com.
nuriwebsoft.co.kr. 2 NS ns231.dnsever.com.
nuriwebsoft.co.kr. 2 NS ns35.dnsever.com.
nuriwebsoft.co.kr. 2 NS ns100.dnsever.com.
nuriwebsoft.co.kr. 2 NS ns259.dnsever.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0