1. A computer-readable storage medium storing a generational garbage collection program used to direct a computer to perform a generational garbage collection process, wherein: the generational garbage collection process comprises a generational garbage collection environment preparing and initializing process; and the generational garbage collection environment preparing and initializing process comprises a process of allocating a single virtual memory space as a virtual memory space of all generations, and distributing the single virtual memory space to each generation such that the virtual memory space of each generation can be continuously arranged in order of generation in the single virtual memory space.