PURPOSE: To make engine control requiring high speed processing effective as well as reduce mounting bases, number of members, and cost, etc., by allowing electric accessories control to interrupt the engine control and the engine control to interrupt the electric accessories control at each prescribed time.

CONSTITUTION: ROM21 of an arithmetic device 17 stores a control program of a CPU19, which includes processing programs such as a main program, an engine control subroutine, and an electric accessory control subroutine, etc. RAM23 stores an input data based on an engine operation state and an electric accessories application state, etc., and arithmetic operation results by the CPU19. The captioned device includes the above-described engine control means 17 for controlling a fuel injection valve in response to the operation state of the engine 31, an electric accessories control means 22 for controlling operations of the respective electric accessories 33 while detecting the application states of said respective electric accessories 33, etc., and a means 11 for generating an electric accessories control interruption signal S1 based on the operations relating to said respective electric accessories 33. Whereas the device mainly operates the engine control means 20, when said signal S1 is inputted, it controls the electric accessories by allowing the operation of the electric accessories control means 22 to interrupt.