An optical transmitting/receiving apparatus capable of suppressing electrical crosstalk and magnetic crosstalk, includes: a laser diode/photo diode (LD/PD) integrated module that terminates a single-core bidirectional optical fiber; a circuit board electrically connected to a lead pin led out of the LD/PD integrated module; and a plastic case that accommodates the circuit board. At least a part of the plastic case abuts against the LD/PD integrated module, and impedance of the plastic case is controlled by mixing a conductive filler into the plastic case.