When a program execution unit of a computer executes a creation instruction of objects utilized by an execution target program in process of executing the execution target program, the program execution unit disposes a created object in an internal heap when a life period of the created object is not contained within life period of objects for root class and gets average value of life time corresponding to set of objects to which the created object belongs with reference to memory allocation information table to dispose the created object as a long-life object in an external heap when the gotten average value of life time is equal to or larger than a predetermined value. Accordingly, life time of objects is measured and long-life objects are not managed by GC, so that program utilizing objects can be executed at high speed.