A receiving device performs log noise amplification on radio waves (desired waves and interfering waves), received with an antenna, to generate a received signal, converts the received signal into an intermediate frequency signal, converts the intermediate signal into a digital signal, filters out and demodulates a frequency band of a specific channel from the digital signal. Herein, a first received signal strength (RSSI 1) is detected from the digital signal, while a second received signal strength (RSSI 2) is detected from the digital signal of the specific channel. The intermediate frequency signal is amplified with a first gain which is calculated by way of the comparative judgment on the first receive signal strength and the allowable threshold. The digital signal of the specific channel is amplified with a second gain.