Apex domains cannot have CNAME records.
Question and response
Question
dig yamaguchi-pu.ac.jp. NS
Answer
yamaguchi-pu.ac.jp. 5 NS ws1.yamaguchi-pu.ac.jp.
Authority
The response has no authority records.
Additional
ws1.yamaguchi-pu.ac.jp. 5 A 202.245.136.130
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0