PURPOSE: To prevent a control unit which is enabled to perform an inspection mode from performing the inspection mode unintentionally.

CONSTITUTION: The control unit 1 is equipped with a microcomputer 2, input terminals 5-7, and output terminals 8-10; and input equipments such as a water temperature sensor 11 are connected and equipments to be controlled such as a warning lamp 12 are connected. This control unit is enabled to execute a normal control mode wherein respective equipments to be controlled are controlled according to the inputs from the respective input equipments and the inspection mode wherein an inspection result signal of the operation of the control unit 1 is outputted from the output terminals 9 and 10. The microcomputer 2 is provided with a decision means 17 which decides the connection of an inspection device and a switching means 18 which switches the normal control mode to the inspection mode. An output signal accompanied by specific variation is inputted from the output terminal 8 and when a signal synchronized with the output signal is inputted to the input terminal 5 at this time continuously for a specific time, the inspection mode is executed.