A communication device includes: a signal reception circuit to receive a differential signal and convert the differential signal into binary data; a squelch detection circuit to compare an amplitude level of the differential signal with threshold voltages to detect presence or absence of a signal and detect a non-squelch state and a squelch state; a start pattern detection circuit to enter a receivable state in response to a predetermined start pattern based on the differential signal; a register that stores a squelch setting value associated with the threshold voltages; a DC voltage selection circuit to select two DC voltages in accordance with the squelch setting value, and supply the two DC voltages to the squelch detection circuit; and a squelch setting control circuit to change the squelch setting value to increase or decrease the squelch setting value in steps and sequentially set the squelch setting value in the register.