To enable the easy capturing/separation of fine dust which can be the cause for allergy and contains a tick, a mildew and the like in a room by using a felt which shows the respective specific values of thickness and density as a filter to be mounted in the suction process of a suction device such as a vacuum cleaner.

A guide 1 is fitted to a pipe part in the suction process of a suction device such as a vacuum cleaner, and a filter 3 is mounted on the guide 1. The method for mounting the filter 3 is preferably to sandwich it between filters 2, 4 of nylon or the like having 10-70 mesh and 10-250 mesh, respectively. The filter 3 to be used is made of a felt with 1-3 mm thickness and 0.1-0.4 g/cm3 density. The felt material to be used is not particularly limited but is preferably a polyester needle punch felt. In the practical use application of the filter, the three filters 2-4 are, for example, fitted into the guide 1 and fixed with screws 5, 6, and further, the guide 1 is mounted on the pipe part in the suction process of the vacuum cleaner.