To obtain a laser beam of high luminance by using a plurality of plate-like laser units each of which has an LD array arranging many laser diodes like a bar.

Two LD unit stacks 3a, 3b obtained by stacking a plurality of plate-like LD units 1 each of which has an LD array 2 arraying many laser diode elements like a bar in a slow axis direction are prepared, collimator lenses 4, 5 setting the width of a laser beam emitted from the LD unit 1 in a fast axis direction to be equal to the thickness of the LD unit 1 or less and setting the width of the laser beam in the slow axis direction equivalent to the length of the LD array 1 are arranged in the front of the stacks 3a, 3b and a PBS(Polarized Beam Splitter) adder 14 consisting of a λ/2 wavelength plate 12 for reducing the width of the a laser beam emitted from each of the lenses 4, 5 to a half and a polarized beam splitter 13 is also arranged.