A master unit and a plurality of slave units perform a multi-hop communication. The plurality of slave units include hybrid slave units are configured to select at least one of wireless communication and power line carrier communication. One hybrid slave unit includes a function of reporting, to the other hybrid slave unit in which a hop number in the power line carrier communication between the one hybrid slave unit and the other hybrid slave unit is one, the minimum route cost when the wireless communication is used for a channel on an upper side. The one hybrid slave unit includes a function of adopting the power line carrier communication when a route cost reported by the other hybrid slave unit is smaller than the minimum route cost of the one hybrid slave unit, and otherwise adopting the wireless communication.