The invention, while reducing noise, suppresses a load increase in a processor and a delay in drive control. An engine control unit includes a processor, a driving circuit including a switching element to drive a load such as a fuel injector and an ignition device, and a communication circuit that transmits control signals from the processor to the driving circuit via serial communication. The control signals each include a command frame for controlling the driving circuit and a data frame for driving the load. If a predetermined bits in each of the data frames received from the processor at predetermined time intervals are determined to be the same twice in succession, the engine control unit changes a state of a driving signal 'Drive' for driving the load and thereby changes an operating state of the switching element.