A plurality of lead pins (2a-d) penetrates through a stem (1) having a circular shape and includes a signal lead pin (2a,2b). A block (4) is provided on an upper surface of the stem. A waveguide light receiving device (9) is provided on a side surface of the block. An amplifier (6) is provided on the side surface of the block and amplifies an electric signal output from the waveguide light receiving device. A first relay substrate is provided on the upper surface of the stem and arranged between the block and the signal lead pin. A first transmission line (12a,12b) is provided on the first relay substrate. A first wire (10f,10g) connects one end of the first transmission line and an output terminal of the amplifier. A second wire (10h,10i) connects the other end of the first transmission line (12a,12b) and the signal lead pin.