Receiving antennas 2a, 2b receive a digital modulated signal from a digital wireless microphone. The digital modulated signal comprises a carrier signal modulated with successively generated digital signal trains. A changeover switch 4 selects one of the antennas 2a, 2b in response to a selection signal. A high-frequency unit 8, a demodulating unit 10 and a decoding unit 12 receive and demodulate the digital modulated signal received by the selected antenna. Analog comparators 24a, 24b compare a reception level indicative signal from the high-frequency unit 8 with threshold values, and a diversity judging unit 28 changes the selection signal in accordance with the comparison result. The digital signal trains comprise a plurality of successive frames, and each frame includes an information data section, a preamble section preceding the information data section for establishing synchronization of the information data section, and a guard bit section succeeding the information data section. Each time the guard bit section is received, the selection signal is changed and the antenna selection is performed.