An interference of control signals is caused by a deviation in the start timings of counting between counters of timer counter units of a first MCU and a second MCU. And thus, when a count value of the counter of the MCU of a parent reaches a predetermined value D, the MCU of the parent transmits a trigger signal to the MCU of a child. The MCU of the child obtains the time difference between the start timings of the counts of the counters of the parent and the child from the difference between the D and a count value E of the child at that time. A count period of the child until a maximum value of the count value is reached is adjusted by the time difference.