To provide a new flange mechanism can improve workability in the attaching/detaching of a fixing nut in the replacing work of cutting blades.

A flange mechanism sandwiches a cutting blade to be fixed at a tip end of a rotatably supported spindle for cut-machining an object-to-be-machined, and has a fixed flange including: a columnar boss part of which an outer circumference of its tip end has a male screw formed; a blade mounting part formed at an intermediate portion in the axial direction of the boss part; and a flange part formed protruding from the rear end of the boss part in the axial direction into the radial direction resulting in supporting the cutting blade, while having a fixing nut of annular shape whose inner circumferential surface has a female thread formed thereon that fittingly screws together with the male thread of the boss part while sandwiching the flange part of the fixed flange and cutting blade for fixing, whereas the mutually screwing male thread of the fixed flange and female thread of the fixing nut are composed of multiple threads, with the starting ends of the multiple threads being formed at an equal interval in the circumferential direction.