To provide a flange mechanism capable of preventing co-rotation of a hold-down flange even when a cutting blade rotates idly.

A flange mechanism 24 holding a cutting blade 21 includes: a fixed flange 25 provided with a boss 25a, a blade mounting part 25b supporting an inner circumferential surface of the cutting blade 21, and a receiving flange part 25c supporting one side surface of the cutting blade 21; a hold-down flange 26 inserted into the boss 25a and holding the cutting blade 21 with the fixed flange 25; a fixing nut 27 screwed with a male screw 25e of the boss 25a and fixing the hold-down flange 26 to the fixed flange 25; and a fitting means 28 comprising a protrusion 28a and a recess for bringing the fixed flange 25 and the hold-down flange 26 into engagement with each other when the cutting blade 21 is held between the fixed flange 25 and the hold-down flange 26 and restricting the rotation of the hold-down flange 26 fixed to the fixed flange 25.