the lens holder frame 23 and are located in front of the lds 20 a through 20 d the collimator lenses 22 a through 22 d collimate the laser light emitted from the lds 20 a through 20 d respectively the prisms 24 a and 24 b are adapted to shift the optical axes of the collimator lenses 22 b and 22 c so as to be aligned in parallel so that the optical axes of the collimator lenses 22 b and 22 c and the optical axes of the collimator lenses 22 a and 22 d are made parallel at the emission surfaces thereof namely the four laser lights passing through the collimator lenses 22 a through 22 d are emitted from the laser unit 11 in parallel and at an equal distance in the vertical direction the positions of the supporting frames 21 a through 21 d which support the lds 20 a through 20 d relative to the lens holder frame 23 are adjusted in the directions x and y in fig4 so that the emission axes of the lds 20 a through 20 d are aligned with the corresponding optical axes of the collimator lenses 22 a through 22 d after adjustment the supporting frames 21 a through 21 d are secured to the lens holder frame 23 by screws fig4 shows the laser unit 11 in which the supporting frames 21 a through 21 d.