the thermal resistance between the ground wiring pattern 72 a and the metallic pattern 75 c and the thermal resistance between the metallic pattern 75 b and the first upper cover 76 a to be lower than that given by an air layer therebetween thus it is possible to restrain the temperature of the laser driver ic 72 to a small value i comparison with the proof temperature of the laser driver ic 72 next explanation will be made of another embodiment of the present invention with reference to fig4 and 5 in the case of the application to an optical pick up 7 fig4 is a plan view partially illustrating a flexible printed board 75 for the optical pick up 7 in this embodiment of the present invention and fig5 is a sectional view partially illustrating a mounting part for the laser driver ic 72 the laser driver ic 72 is mounted on the flexible printed board 75 by soldering 79 on the side which is rear of the sheet surface of fig4 the laser driver ic 72 is attached thereto with a heat spreader 72 a in order to dissipate a heat generated from an internal chip in this embodiment the heat spreader 72 a and the ground wiring pattern 75 a of the flexible printed board 75 are electrically and thermally connected.