To find a contaminated state of a filter at a glance and to easily exchange it by sticking the filter on the whole surface of a suction hole of an air conditioner to use it.

In the case that the filter 1 is attached to the air conditioner 3, paper on a self-adhesive tape 2 on the back of the filter 1 is taken off and the filter 1 is stuck to the whole surface of the suction hole 14 of the air conditioner 3 with an easy work. Since a contaminated state of the filter 1 can be found from the outside of the air conditioner 3 at a glance, the exchange time is definitely determined, and troubles such as generation of malodor and scattering of mold, etc., into a room caused by use of it in a contaminated state for a long period are eliminated. Exchange to a new filter 1 is completed by peeling off an old filter 1 from the suction hole 4 of the air conditioner 3 and the new filter 1 is stuck. Thus, the exchange of the filter is easy and this air filter can be used regardless of the maker and a kind of the machine and also has dust removing effect, deodorizing effect and sterilization effect, etc.