Air filter

An air filter comprising:

• a filter element having a pleated filtering portion and a collar portion that extends on an outer periphery of the filtering portion and that has a sealing function, the filtering portion and the collar portion being integrally formed from a same material;
• a cap and a case each of which has a flange for clamping the collar portion of the filter element;
• a protruded portion formed in one of the flange of the cap and the flange of the case, the protruded portion having a first inclined portion;
• and
• a recess portion formed in the collar portion of the filter element, the recess portion fitting to the protruded portion at a predetermined position so as to become set in position,
• wherein one of an inside surface of the recess portion and an outside surface of the recess portion contacts the first inclined portion of the protruded portion and is guided by the first inclined portion, and the other one of the inside surface and the outside surface is pressed by the protruded portion so as to seal a gap between the protruded portion and the recess portion.