To prevent the drop-out and the cracking of a cleaning brush.

A contact section 52 of the cleaning brush 50 is inserted into an opening 61 from the brush contact surface 60a side of a brush presser member 60, the contact section 52 is directed opposite from an installation base 40, and then the brush presser member 60 is set in an installation recessed part 43 of the installation base 40, thereby pressing the cleaning brush 50 against the installation base 40 by means of the brush presser member 60. Under this condition, insertion holes 61 formed in the brush presser member 60, insertion holes 511 formed in the cleaning brush 50, and insertion holes 431 in the installation recessed part 43, communicate with each other. By inserting fixation pins 70 into the insertion holes 431 via the insertion holes 62 and the insertion holes 511, the cleaning brush 50 can be fixed while it is pressed against the installation base 40. In the cleaning brush 50, one surface 51 of a flat section 51 and a side face 52a of the contact section 52 are connected to each other by a curved face 53.