A device includes: a wireless power receiver configured to receive wireless power from an external device external to a body; a capacitor configured to store therein the wireless power received by the wireless power receiver; a wireless transceiver configured to transmit, to the external device, information associated with stored energy of the capacitor and scheduled energy to be used; and a processor configured to operate with the stored energy of the capacitor and process a biosignal of the body, wherein an operation of the external device and an operation of the device are synchronized, and a wireless power quantity of the wireless power to be received by the wireless power receiver from the external device is determined based on the information transmitted from the wireless transceiver to the external device.