PURPOSE: To obtain easily a uniform and optimum exposed image by executing the adjustment of parallel degree of a platen glass and focusing of an exposed image by the same operation.

CONSTITUTION: One end of a platen glass 11 is held so as to be slidable on a platen guide plate 15 fixed with a screw 19 to a body frame 14a, and the other end of the platen glass 11 is held on a platen glass holding frame 16, and supported by a rail supporting plate through a platen sliding rail 17. Also, in order to adjust a parallel degree and its height against a photosensitive drum 12 of the platen glass 11, a rail supporting plate 18 for supporting the platen glass 11 through the platen sliding rail 17 is fixed to a body frame 4b through a fitting position adjusting member 20.