PURPOSE: To recover a microcomputer in runaway in the minimum time by using a preset counter as a runaway detecting counter so as to set optionally the runaway detecting time of a counter with a software.

CONSTITUTION: In a normal state, a preset counter 2, before the number of clock signals 4 counted by the counter 2 coincides with a preset value, is reset by inputting a reset signal 3, the reset interval time of which is fixed with the software, from a microcomputer system part 1 to the preset counter 2. When the microcomputer part 1 runs away, the preset counter 2 outputs a signal 6 which resets the microcomputer system part 1 by a coincidence between the preset value and the counted value of the clock signal 4 due to no input of the reset signal 3 from the microcomputer system part 1 to the preset counter 2. In this way, the microcomputer can be recovered in the minimum time from a runaway state.