To send battery information in real-time to a charging pad on the power supply side, though with a simple circuit configuration.
A device housing a battery and a charging pad comprises a device 50 housing a battery including a receiving coil 51, and a charging pad 10 including a transmitting coil 11 that magnetically couples with, and supplies charging power to the receiving coil 51. The device 50 housing the battery further includes a modulator circuit 61 that changes the impedance of the receiving coil 51 according to battery information of an internal battery 52. The charging pad 10 further includes a detection circuit 17 that detects receiving coil 51 impedance changes to detect the battery information. The modulator circuit 61 has a load circuit 62 that is connected in parallel with the receiving coil 51 and has a switching device 64 series-connected to an impedance modulating capacitor 63, and a control circuit 65 that switches the load circuit 62 switching device 64 ON and OFF according to the battery information. The modulator circuit 61 switches the switching device 64 ON and OFF to transmit battery information to the charging pad 10.