Apex domains cannot have CNAME records.
Question and response
Question
dig aams5.jp. NS
Answer
aams5.jp. 4 NS www1.aams.jp.
aams5.jp. 4 NS www2.aams.jp.
Authority
The response has no authority records.
Additional
www1.aams.jp. 4 A 210.134.179.218
www2.aams.jp. 4 A 210.134.179.219
www1.aams.jp. 4 AAAA 2001:278:1047:410:0:0:0:218
www2.aams.jp. 4 AAAA 2001:278:1047:410:0:0:0:219
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0