PURPOSE: To guarantee the execution of the diagnostic processing with high reliability by an electronic controller by executing a diagnostic processing till the time designated by diagnostic continuation time information reaches and terminating the diagnostic processing when the designated time reaches.

CONSTITUTION: A CPU 11 executes a prescribed calculation based on the sensor data fetched by a RAM 13, determines fuel injection quantity every time and executes the delivery and reception of a communication message with a diagnostic tool 5 and a designated and prescribed diagnostic processing, in accordance with the control program which is preliminarily stored in a ROM 12. The diagnostic processing is executed till when the time designated by the diagnostic contiuation time information of the communication message reaches. When the time designated by this diagnostic continuation time information reaches, the diagnosis in execution is terminated.