A program parallelization apparatus which generates a parallelized program of shorter parallel execution time is provided. The program parallelization apparatus inputs a sequential processing intermediate program and outputs a parallelized intermediate program. In the apparatus, a thread start time limitation analysis part analyzes an instruction-allocatable time based on a limitation on an instruction execution start time of each thread. A thread end time limitation analysis part analyzes an instruction-allocatable time based on a limitation on an instruction execution end time of each thread. An occupancy status analysis part analyzes a time not occupied by already-scheduled instructions. A dependence delay analysis part analyzes an instruction-allocatable time based on a delay resulting from dependence between instructions. A schedule candidate instruction select part selects a next instruction to schedule. An instruction arrangement part allocates a processor and time to execute to an instruction.