PURPOSE: To reduce the execution time of a management program and to reduce the load of a central processor, by peforming the priority control with the monitor of an execution time of each program without using the management program.

CONSTITUTION: At a start time 1 of a program executing period at a central processor of a computer, a start preparation 2 of a program A is requested to a management program P, and the time count of an execution time monitor program S is zeroed. The count is incremented by (1) at the prescribed periods 22, 23 of the execution time T, and after the program A is executed at the execution 21, the execution is transferred to the execution 24 of the program B directly without being transferred to the program P. When the rest time is less than the execution time of the program B, the end processing is requested to the program P to reduce the executing time of the program P, allowing to reduce the load of the central processor.