A radio transmitter includes a radio module alternately repeating a communication mode in which power is consumed to wirelessly transmit predetermined information and a standby mode in which standby power is consumed with no radio transmission performed, and a power supply section supplying power to the radio module. The power supply section includes a secondary battery storing power, a solar battery converting light energy into power, and a charging circuit controlling power supply from the solar battery to the secondary battery and power supply from the secondary battery to the radio module. The charging circuit feeds power from the solar battery to the secondary battery during a period of the standby mode.