A battery monitoring apparatus to monitor a state of a battery comprising one of one battery cell and a plurality of battery cells connected in series, the apparatus comprising: a reception section configured to receive a radio signal transmitted from a controller and to output power gained through the radio signal wherein the radio signal is encoded with ID information and command information to designate the contents of a monitoring operation, and wherein the reception section is configured and wherein the reception section is configured to demodulate the received radio signal and output the demodulated radio signal; a first power source circuit configured to supply power to a decode circuit based on the power outputted from the reception section; the decode circuit containing inherent ID information and is adapted to operate upon receiving the power supply from the first power source circuit and to perform authentication for confirming whether or not the received radio signal is that transmitted from the controller to the battery monitoring apparatus by comparing the ID information contained in the demodulated signal outputted from the reception section with the inherent ID information, wherein the decode circuit is configured to output the command information of the demodulated signal to a battery monitoring circuit when the ID information contained in the demodulated signal corresponds to the ID inherent; the battery monitoring circuit is configured to output a monitoring result of a state of the battery according to the command information outputted from the decode circuit; a transmission section to wirelessly transmit the monitoring result outputted from the battery monitoring circuit to the controller; and a second power source circuit configured to supply power to the battery monitoring circuit and the transmission section based on power of the battery; wherein the decode circuit is configured to output an activation signal to the second power source circuit when the ID information contained in the demodulated signal corresponds to the ID inherent and a second power source circuit is activated according to the activation signal outputted from the decode circuit so as to start supplying power to the battery monitoring circuit and the transmission section, wherein when the activation signal is not outputted again from the decode circuit to the second power source circuit by a time when a prescribed time-out duration has passed since the second power source circuit is activated, the second power source circuit is configured to halt power supply to the battery monitoring circuit and the transmission section. a reception section configured to receive a radio signal transmitted from a controller and to output power gained through the radio signal wherein the radio signal is encoded with ID information and command information to designate the contents of a monitoring operation, and wherein the reception section is configured and wherein the reception section is configured to demodulate the received radio signal and output the demodulated radio signal; a first power source circuit configured to supply power to a decode circuit based on the power outputted from the reception section; the decode circuit containing inherent ID information and is adapted to operate upon receiving the power supply from the first power source circuit and to perform authentication for confirming whether or not the received radio signal is that transmitted from the controller to the battery monitoring apparatus by comparing the ID information contained in the demodulated signal outputted from the reception section with the inherent ID information, wherein the decode circuit is configured to output the command information of the demodulated signal to a battery monitoring circuit when the ID information contained in the demodulated signal corresponds to the ID inherent; the battery monitoring circuit is configured to output a monitoring result of a state of the battery according to the command information outputted from the decode circuit; a transmission section to wirelessly transmit the monitoring result outputted from the battery monitoring circuit to the controller; and a second power source circuit configured to supply power to the battery monitoring circuit and the transmission section based on power of the battery; wherein the decode circuit is configured to output an activation signal to the second power source circuit when the ID information contained in the demodulated signal corresponds to the ID inherent and a second power source circuit is activated according to the activation signal outputted from the decode circuit so as to start supplying power to the battery monitoring circuit and the transmission section, wherein when the activation signal is not outputted again from the decode circuit to the second power source circuit by a time when a prescribed time-out duration has passed since the second power source circuit is activated, the second power source circuit is configured to halt power supply to the battery monitoring circuit and the transmission section.