To provide a drift-prevention valve device, a blade device, and a working machine capable of operating an actuated unit and preventing the machine body from drifting with a simple configuration. The drift-prevention valve device is provided with a non-return valve 41 that allows the flow of hydraulic oil from a control valve 28 to a head chamber 34h of a blade cylinder 34 and blocks the flow of the hydraulic oil in the reverse direction; and a piston accommodation part 42 separately disposed from an accommodation part 70 of the non-return valve 41, configured to movably accommodate a power piston 43. The power piston 43 defines a first piston chamber 42p1 communicating with a rod chamber of 34r of the blade cylinder 34 and a second piston chamber 42p2 for drain positioned on a poppet 71 side of the non-return valve 41 and communicating with a tank 52. The power piston 43 is connected to the poppet 71 of the non-return valve 41, so that the power piston 43 can be operated by the difference between the urging force of the poppet 71 by a spring 72 of the non-return valve 41 and a rod chamber pressure of the blade cylinder 34.