A state function which describes some quantum phenomenon includes two types of information in a mixed form: the information on the probabilistic behavior and also on the physical state of the system. The aim of this paper is to show that it is possible to separate the probability information from the description of a quantum process. This is done by applying the consistent history method by Griffiths, Omnes, GellMann, and Hartle to the path-integral formulation. The remainder should be an elementary physical process, the realization of which presumably obeys the law of probability.