To provide a machining device for a light alloy wheel for accurately machining a valve hole without causing external appearance failure even in the light alloy wheel narrow between spokes.

This machining device for the light alloy wheel has the cutting function for machining the valve hole and the fixing function for fixing the light alloy wheel. The machining device has the detecting function for detecting a turning angle of the fixed light alloy wheel, and is characterized in that the fixing function has a gripping means for gripping the light alloy wheel, and a means for axially rotating the gripped light alloy wheel.