A transmission unit includes a transmission pulse signal generating circuit which generates a transmission pulse signal having pulses corresponding to a plurality of clock signals generated in a clock signal generating circuit, existing between a first pulse and a second pulse which are generated in an edge pulse generating circuit. A receiving unit is configured to decode a received pulse signal based on the transmission pulse signal received from the transmission unit via an isolated communication unit, as a signal that transitions from a first level to a second level when an initial pulse of the received pulse signal is detected and that transitions from the second level to the first level when a subsequent pulse is not detected within a predetermined first time period from when a most recent pulse of the received pulse signal is detected.