A receiving device is provided. The receiving device includes an antenna device, a filter circuit, a transceiver, an adjustable attenuator, a circulator, and a processor. The antenna device receives a received signal. The filter circuit separates an in-band signal and an out-band signal from the received signal. The adjustable attenuator adjusts the attenuation value corresponding to the in-band signal and transmits the adjusted in-band signal to the transceiver. The circulator receives the received signal from the antenna device and transmits the received signal to the filter circuit, and the circulator receives a reflected signal from the filter circuit. The processor determines how to adjust the attenuation value corresponding to the in-band signal according to information related to the out-band signal and information related to the in-band signal that has been processed by the adjustable attenuator and the transceiver.