[Help] Exposure problem on Eos 50D

[martingundul]

Guys, I got a problem with my canon 50D exposure.
Whenever I shot the camera with shutter speed more than 1/320, I'll get unstable result, which are having a dark horizon on the pictures, moving from bottom to upper side, from one picture to another, respectively.
ISO setting and the aperture I was using are relatives, but this seems to be even worst in the higher ISO setting and higher shutter speed.
This following picture was taken from continuously from left to right, up to bottom.

Please help me with this matter, if maybe somebody out there knows or ever has the same problem with me.

Thanks, and best regards
Martin