A mechanism for recording a timing in which a high urgency process is started is provided, and upon entry to a critical section in the middle of a low urgency process, by referencing the record, it is inspected whether a high urgency process will be started during execution of the critical section. If it will not be started, the critical section is entered, and if it will be started, control is exerted so that entry to the critical section is postponed until the high urgency process is completed. Exclusive access control in a critical section can be performed suitably under conditions where a plurality of task execution environments exist.