PURPOSE: To easily perform a dust removing operation by operating the operating time of a shaker motor as a filter vibrating means and driving it according to an operation cumulative time timed on a main motor driven by a blower.

CONSTITUTION: At the time of the operation of a main motor 11 as the driving means of a blower 3, the operation cumulative time of the motor 11 is timed by a controller as a timing means. Then, the motor 11 is driven for more than a prescribed time. When the switch of the motor 11 is turned off, the operating time of a shaker motor 6 which is the vibrating means of a filter 5 is operated by the controller on the basis of the operation cumulative time of the motor 11 and the shaker motor 6 is driven during the operated time. Thus, the high filtering efficiency of the filter 5 can be constantly maintained.