PURPOSE: To clean the backing roll, calender roll, or the like, of a coater without the generation of vortexes and splashes of cleaning water.

CONSTITUTION: A doctor blade 4 is mounted to a blade holder 3 freely regulatably relatively to the surface of the roll 1. A water injection pipe 2 is arranged in the front part of the doctor blade 4 relatively to the rotating direction of the roll in order to supply the cleaning water to the surface of the roll 1. A rubber sheet 5 or guide blade extending to the corner angle part between the doctor blade 4 and the roll 1 is disposed so as to come into tight contact with a nip 8 between the roll 1 and the doctor blade 4. The end edge of the rubber sheet or the guide blade is extended over the entire length of the doctor blade. The cleaning water flowing back from the surface of the roll is guided by this end edge, by which the cleaning water colliding against the doctor blade is controlled and the vortexes and splashes of the cleaning water generated by the rotation of the roll are prevented.