PURPOSE: To facilitate the cleaning of an air filter by providing a rack along the vertical direction of a suction grill while the main body is provided with a pinion gear to be meshed with the rack and a motor for rotating the gear to allow opening or closing of the suction grill.

CONSTITUTION: A rack 22 is provided along the vertical direction of a suction grill 21 while the main body 20 is provided with pinion gears 25 and 26 to be meshed with the rack 22 and a motor for rotating the gears. When the pinion gear 25 is rotated normally by the motor, with the lowering of the rack 22, the suction grill 21 moves askew downward with respect to the main body 20 and the moment a stopper 23 hits a member such as the pinion gear 25 or a limit switch, the motor or the rack 22 is stopped. Under such a condition, an air filter 27 is taken out of the rear of the suction grill 21 to clean up.