Help identifying Jupiter 21M lens mount

Hello

I have a Jupiter 21M 4/200 Serial number 84012071 lens I bought recently on impulse.

I dont recognize the mount?

Any feedback most welcome

http://www.ussrphoto.com/resize/resize_image.aspx?ImgWd=800&IptFl=/UserContent/2752017_05270002 Jupiter Lens.jpg

http://www.ussrphoto.com/UserContent/2752017_05270002 Jupiter Lens.jpg

This is lens with adapter to modern digital camera. The adapter is put on the lens.
For me it looks like Canon EF or Minolta/SONY A bayonet.

Bus shape of the gold contacts tells me this ic Canon EF. [:)]

Alfa mate - thanks for the correct answer

I tried previously removing this mount but it was on that tight I gave up assuming (foolishly) that Jupiter must have made this lens with another mount other than the the standard M42. So I went at this mount again and hey presto it un-tightened revealing the M42 thread -all's well in Nirvana again

Welcome [;)]

Hello and welcome to the forum Broto.