A single-fiber bidirectional optical transmitter/receiver includes a single-fiber bidirectional optical transmission/reception device. A circuit board has a signal processing circuit and a drive circuit configured to drive the single-fiber bidirectional optical transmission/reception device. A main housing accommodates the single-fiber bidirectional optical transmission/reception device and the circuit board. A ground part of a reception side of the single-fiber bidirectional optical transmission/reception device is electrically connected to a ground part of a transmission side of the single-fiber bidirectional optical transmission/reception device through a ground wiring pattern formed on a flexible printed board.