Based on size and shape (6" long and fairly robust) I would say it belonged to a small stocky animal. And since you found it in central Europe, one of the most common animals to fit the bill would be a wild pig or boar of some type. Possibly an immature one.
I googled some pictures of pig bones and it looks like it might be the upper arm (front leg) bone (Humerus).
In order to narrow it down it would be helpful to see it in perspective as Farmerman suggested. But it would really help to date it (even an approximate age would eliminate a lot of possibilities) and cross section it to see if it's a mammal bone or something else.
In a very general sense, there's a much higher probability that you would find a bone from a common animal than a rare one. And it's more likely that you would find something recent than something extremely old. Based on those two things alone and the visuals, I would guess Pig or Hog. But it's just a guess.