A microprocessor which is adapted to start a second task at a predetermined time when a first task is running if a current time becomes to be equal to the predetermined time is disclosed. The microprocessor executing an instruction read out from a program address updated every time when each execution of instruction is completed, includes update ceasing means for ceasing the program address from being updated when an stopping time comes in order to abort a first task defined by a first computer program and overwriting means for overwriting the program address with an initial address of a second computer program when a predetermined time comes in order to start to execute a second task defined by the second computer program at the predetermined time.