Tokyo, June 29, 2016 (AFP) - A Japanese judge who posted photos of himself half-naked and bound with ropes on Twitter has apologised for being "inappropriate".

Tokyo High Court judge Kiichi Okaguchi, 50, was ticked off by bosses after uploading the bondage snaps of himself wearing only perfectly legal briefs.

"An S&M queen comes to a bar after closing hers," he explained in a tweet accompanying the risque pictures, reportedly taken in the establishment.

"So I became a guinea pig and was tied up."

High court director Saburo Tokura was not amused, and administered a stiff rebuke for "posting inappropriate tweets", a spokeswoman told AFP on Wednesday.

Okaguchi, a graduate of the prestigious University of Tokyo and author of several manuals on civil law, said he was sorry "for causing trouble".

He also vowed to never post such tweets again, and will apparently keep his job.