An air filter essentially for use in woodworking workplaces includes a casing having a top panel, a bottom panel, two sidewalls, a filter gauze, a motor, and whizzer blades. The casing has an inlet anteriorly and an outlet. The casing has therein an inner blocking wall which extends rearward to form two inner sidewalls. The two inner sidewalls are each penetrated by a through hole. The two through holes face each other. The casing further has a curved panel bending in its thickness direction. The curved panel and the two inner sidewalls together define a receiving space. The curved panel curves to an extent corresponding in curvature to part of the outer edges of the whizzer blades and is spaced apart from the whizzer blades by a predetermined distance.