A method for assembling a laser apparatus which condenses a laser beam and couples the laser beam to an optical fiber. After the optical fiber is fixed to a package, the whole or a part of an optical condensing system is fixed to the package through a fixing structure having at least one guide surface extending in at least one of first and second directions respectively parallel and perpendicular to the core axis of the optical fiber, by moving the whole or the part of the optical condensing system along the at least one guide surface to a predetermined position with respect to the core axis, and fixing the whole or the part of the optical condensing system to the fixing structure at the predetermined position.