An adsorption filter for an air cleaner for an internal combustion engine is mounted by being inserted inside a second housing along a face of the adsorption filter. In an inner face of the second housing, the adsorption filter is guided to a mounting position in an inserting direction of the adsorption filter. While the movement of the adsorption filter to the mounting position is allowed by elastic deformation, the adsorption filter is restricted from falling off from the mounting position.