To provide a light source device having an adjustment mechanism in which the correction of the inclination of an optical axis and the adjustment of a focal length in the light source device alone are possible and also a similar correction and adjustment by using tools, etc., are possible even after the device is assembled to a write device.

The base part of a light emitting element 1 is adhered on a spot facing part 2b located approximately at the center part of a light source holder 2. A lens 3 is adhered to the level difference part 4b of a through hole 4a opened at the roughly central part of the lens holder 4 by being abutted with the part 4b. The lens holder 4 and the light source holder 2 are fastened by at least three set screws 6 by leaving a prescribed space between them while holding a compression spring 5 between them. When the convergent positional spot PF1 of a light emitting point PL does not agree with a target position PFO due to the adhesion errors of the lens 3 and light emitting element 1, the spot PF1 can be shifted by changing the fastening of the three set screws 6.