On the other hand, an upper surface electrode of thesemiconductor laser array 7 is electrically connected to the second lead frame 6 by a method such as wire bonding using the wire 8 made of a material such as gold (hereinafter, Au).Meanwhile, plate thicknesses of the first lead frame 5 and the second lead frame 6 are selected so as to satisfy a following equation. a>b<a+c, wherein a: plate thickn