An optical transmitting/receiving apparatus which can suppress electrical crosstalk and magnetic crosstalk is provided with a laser diode/photo diode (LD/PD) integrating module terminating a single-core bidirectional optical fiber; a circuit board electrically connected to a lead pin extracted from the LD/PD integrating module; and a plastic case for storing the circuit board. At least a part of the plastic case abuts to the LD/PD integrating module, and impedance of the plastic case is controlled by mixing of a conductive filler.
