A communication system includes a first communication device that operates using a battery as a main power source and a second communication device that communicates with the first communication device. The second communication device includes a second high-speed data communication unit including a second data communication antenna and a second short-range communication unit including a second magnetic-field antenna for short-range communication. The first communication device includes a first short-range communication unit including a first magnetic-field antenna and a first high-speed data communication unit including a first data communication antenna. When an electromotive voltage of the battery lowers, switches are turned OFF and electric power from a power conversion circuit including a rectifying circuit and a DC-to-DC converter is supplied to a communication controller.