do thai nationals need visa for  entering japan ?

Hello barrywhite,
According to the Japanese Ministry of Foreign Affairs, all foreigners
must possess a valid passport and a visa if they want to enter
Japan[1], with the exception of nationals from 63 countries in which
Japan had a Reciprocal Visa Exemption Arrangements.  Thailand is not
on the list of those nations.  Furthermore, the Japanese embassy in
Thailand provided a visa application form that Thai nationals can fill
out[2].  For more information, please contact the Japanese embassy in
Bangkok at:
Address: 1674 New Petchburi Road, Bangkok 10320 
Tel: 0-2252-6151-9 
Fax: 0-2253-4153 
or their consular post in Chiang Mai:
Address: Unit 104-107, Airport Business Park, 90 Mahidol Rd.,
T. Haiya, A. Muang Chiang Mai 50100, Thailand 
Tel: (053) 203-367 
Fax: (053) 203-373 

I hope that this is the answer you're looking for.  If you need
clarification, please request for it before rating this answer.
secret901-ga

Sources:

1. A Guide to Japanese Visas
http://www.mofa.go.jp/j_info/visit/visa/02.html

2. Japanese embassy in Thailand
http://embjp-th.org/
Visa Application Form:
http://embjp-th.org/img/visaform.pdf

Search strategy:
Japanese embassy Thailand

Hi,
The information posted should be correct. However; in common practice,
it seems Thai national needs to have some kind of guarantee as well,
such as your bank deposit guarantee, invitation from Japanese company
if you are traveling on business etc, unless you are traveling on
tour. This may depend on which embassy you are applying, but it seems
to be this way at least at Japanese embassy in Bangkok.
This is rather unfortunate, but it seems to have started some ten
years back when number of illegal Thai immigrants became high.
Good Loch and have a good trip.
Masaki