An engaging groove (47) with which a gasket (42) is engaged is provided in each of a front side projecting portion (44) and a rear side projecting portion (46) formed in a filter accommodating cylinder (37) to be positioned on an outer peripheral surface (44A, 46A) of each projecting portion (44, 46). Therefore, when the gasket (42) latches on each of the projecting portion (44; 46) to be fitted thereon from an outside, the gasket (42) can be engaged with the engaging groove (47) provided in each of the projecting portions (44, 46). In consequence, at the time of mounting and removing the filter accommodating cylinder (37), the falling-off of the gasket (42) can be prevented, and, for example, an inspection operation, a cleaning operation and the like of an accommodated particulate matter removing filter (41) can be easily performed.