When a heat radiating plate 100 is 27 mm square shape, the recessed portion 130 of the heat radiating plate 100 roughly has a longitudinal dimension of 20 mm, a transverse dimension of 20 mm and a depth of 1 mm; and, the width of the flange portion 120 is about 3 mm.The storage tray 6a shown in FIG. 4 is made of material including ABS resin or the like and an antistatic agent or the like.