| 摘要 |
PROBLEM TO BE SOLVED: To accurately detect the level of accumulated dust without soiling and damaging a level switch with the dust and without performing troublesome maintenance, when the level of the accumulated dust dusted off to the dust box from a filter is detected by using the level switch, and to easily and sanitarily perform the treatment of the dust accumulated in the dust box without deteriorating the environmental condition. SOLUTION: A housing bag S for recovering the dust DS dusted off from a filter 10F, made of transparent plastic, is stored in the inner part of the dust box 13 provided below a dust collector 10, window parts 13X and 13Y formed by using a transparent plate are provided at both left and right side walls of the dust box 13. A light beam type level switch for detecting the level of the accumulated dust DS at the state that the level switch is positioned to the window parts 13X and 13Y is provided.
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