To provide a method where, to a light alloy cast component, a cast skin feeling is smoothly changed to almost whole the surface of the cast component by changing the stroke (distance) of the working materials to be collided, and further excellent mechanical properties can be imparted thereto.

A light alloy cast component (aluminum wheel 10 for a vehicle) is fixed to the inside of an oscillation vessel 12 in such a manner that the distance in the upper and lower directions between the surface of the light alloy cast component and the inside face of an oscillation vessel 12 is gradually changed. Further, working materials including spherical bodies 16 with a size of 1.5 mm to 8 mm are stored in the oscillation vessel 12, the oscillation vessel 12 is oscillated, and the working materials are collided against the surface of the light alloy cast component.