PURPOSE: To simplify the operations of mounting or demounting of the filter by elastically connecting and supporting the driving shaft and follower shaft of an endless belt-shaped filter to the support section of a support plate in extensible shape by an elastic member.

CONSTITUTION: An outer frame 7 on the driving shaft 5 side is moved inwards against the force of a spring 9, and projected from the projecting section 15 of the support plate 14. A connecting section 6 is extracted by a motor shaft, and the driving shaft 5 is removed. The follower shaft 10 is removed similarly. The filter 17 is removed. Mounting is executed in accordance with reverse procedure. According to said constitution, the mounting or demounting of the filter can be simplified.