In order to provide a communication system which performs a communication while maintaining high voltage insulation, a control circuit which is operated at a low voltage, and a controlled circuit which is operated at a high voltage are connected through a propagation layer having a waveguide structure, thereby performing a communication. In particular, a displacement current (surge current) flows between a high voltage circuit and a low voltage circuit due to a potential fluctuation which occurs in the high voltage circuit A surge current protection circuit is provided, and applying of an input which is out of rating to the communication module and the low voltage circuit due to such a surge current is prevented.