To carry out a certain cleaning work while preventing a smudge from adhering to a cleaning mechanism itself before the smudge adheres to a cleaning member and keeping the clearance between the cleaning member and a transparent member with a predetermined value in the cleaning work for the transparent member (dust-proof glass).

When the dust-proof glass 48 is cleaned, a covered part 53 is engaged with the engaging part of an optical scanner, and then the cleaning member 51 is inserted. The tip part of the cleaning mechanism 50 is guided by a plurality of guide parts 54 which are arranged with a fixed spacing in the longitudinal direction and then moves, then the dust-proof glass 48 is cleaned. The cleaning mechanism 50 is formed with the length longer than the one of the dust-proof glass 48 in the longitudinal direction. In the tip part, the width of a recess 52a is made wider than the one of the cleaning member 51 in the side of the cleaning member 51. Thereby, only the area of a laser beam emitting outlet of the dust-proof glass 48 which is cleaned by the cleaning member 51 is connected, and the part other than the cleaning member 51 is prevented from contacting. The smudge is prevented from adhering to the part other than the cleaning member 51 of the cleaning mechanism 50 and then re-adhering to the dust-proof glass 48.