In order to suppress an increase in the processor load and a delay in the drive signal while implementing a countermeasure against noise, an engine control unit has: a processor; a drive circuit containing a switching elements that drive loads such as a fuel injection valve and an ignition device; and a communication circuit that transmits a control signal from the processor to the drive circuit by serial communication. The control signal includes a command frame for controlling the drive circuit and a data frame for driving the load. When prescribed bits in a data frame received from the processor in a prescribed time interval are the same twice in succession, the engine control unit changes the drive signal "Drive" for driving the load, thereby changing the operational state of the switching element.