In an image forming apparatus (1) utilizing electrophotographic technology, position and posture of a laser scan unit (5) with respect top a frame (13) is adjusted easily without cost rise and upsizing of the apparatus. Semicircular recesses (53) and an elongate hole (54) are formed at each of three fixing portions (52a, 52b and 52c) in the vicinities of side faces (51b) and a rear face (51c) of a housing (51) of the laser scan unit (5), and an adjuster 30 serving as a spacer is attached to each of the fixing portions (52a, 52b and 52c). Each adjuster (30) is elected among a plurality of kinds of adjustors respectively having different thicknesses manufactured by press working of metal plates commercially produced and having different thicknesses with using the same dies. The adjustor has a pair of semicircular engaging portions 30b and a coupling portion 30a perpendicular to and coupling the engaging portions (30b).