Patent ID: 7753981

Claim:
A filter unit comprising: a filter medium that has been pleated, and a frame that supports circumference of the filter medium, wherein the frame has a protruding part on at least one face selected from an upper face and a lower face thereof, with the protruding part being formed by allowing a part of the at least one face to protrude, the upper face is a surface of the frame that faces an upstream side relative to a flow of air that passes through the filter medium, the lower face being a surface of the frame that faces a downstream side relative to the flow of air, fitting portions with a concave shape and/or a convex shape being formed at four side faces that form an outer periphery of the frame, two side faces opposing each other having shapes that allow a fitting portion of one of the side faces to fit to that of the other of the side faces, fitting portions of the two side faces opposing each other being provided with a convex shape that matches a concave shape of the opposed side face and a concave shape that matches a convex shape of the opposed side face, a cross-sectional shape of a fitting portion of one side face of the outer periphery of the frame being identical to that of a fitting portion of one selected from two side faces adjacent to the one side face, and the protruding part being provided to surround the filter medium when viewed from a direction perpendicular to the surface of the frame having the protruding part, wherein the protruding part is formed in a position nearer to the outer periphery than to an inner periphery of the frame.