A bi-directional optical wireless communication apparatus comprises a modulator outputting a narrow band signal whose center frequency is selected from N center frequencies, an optical transmitter transmitting an optical signal from the narrow band signal, an optical receiver for receiving N optical signals, N receiving circuits corresponding to the N center frequencies, a cancelling circuit for cancelling the optical signal received by the optical receiver via reflective object in received N optical signals using the narrow band signal in accordance with a magnitude of the optical signal received by the optical receiver, a frequency discriminator discriminating frequencies of the received N optical signals, and a control circuit. The frequency discriminator discriminates for an interval that the optical transmitter does not transmit the optical signal. Then, the modulating circuit continuously outputs a received signal from one of N receiving circuits corresponding to the discriminated frequency and the modulator modulates the narrow band signal to have a center frequency other than the discriminated frequency under control of the control circuit. The interval is repeated with a repetition randomly set interval.