Who judges Karma?

I know the Buddhism does not believes in the existence of personal god.But if it is the case that there is no personal God who is capable of interacting with his own creation,then who/how to determine(s) whether a person/creation has done/involved something which can be treated as bad/good aspects of *Karma* ? In Buddhism *Karma* refers to the actions driven by intention which manifested itself in physical, vocal or mental form which leads to future consequences(having a moral character).Also the cycle of rebirth determined by this *Karma*. If this decision is made at the end of one's life,who/how are these decision made by an impersonal force.How can these forces do anything?Doesn't it necessarily requires a 'personal being' to judge?And who is the final judge of a *Karma*?