To provide a fog effector which enables high-speed fog processing of appropriate accuracy corresponding to a case.

A fog effector circuit 2 performs fog processing to a fragment located on a three-dimensional image space in a ratio corresponding to that location. The fog effector circuit 2 is composed of a ROM table for defining a distance Z between the point of view in the three-dimensional image space and the fragment to be displayed, color information Cf of fog, color information Ci of the fragment and parameters density, start and end for affecting the other fog effect as input parameters and defining color information provided by the fog processing to the fragment as output data.