To provide a machining device and a machining method of a light alloy wheel free to produce a wheel favorable in precision even in mass production and to provide the light alloy wheel from a bead seat part of which deflection is especially reduced by them.

The wheel molded of a material by casting a wheel diameter of which is more than 16 inches and the deflection of the bead seat part of which is less than 0.2 mm is manufactured by machining an offset surface of the wheel material, fixing the offset surface of this wheel material on the machining device as a machining standard part and lathe-machining an outer peripheral surface of its rear rim part.