A master calculator assigns a series of processing groups to a communicable worker calculator. The master receives information about an execution time and a waiting time from the worker calculator for the series of processing groups. The computer acquires the time elapsed between transmitting the processing group transmitted to the worker calculator and receiving the execution result of the processing group from the worker calculator. The master calculates the communication time required for communication with the worker calculator on the basis of the information received and the elapsed time acquired. The master calculates the number of processings to be assigned to the worker calculator on the basis of the communication time calculated. The master generates a processing group to be assigned to the worker calculator on the basis of the number of processings calculated, and transmits the processing group generated to the worker calculator.