Abstract: In order to render a three-dimensional space which has a spotlight source with a cone angle .theta. at high speed and with better quality, an object's surface in the three-dimensional space is first meshed into a plurality of elements. Then, a radiosity from the spotlight source is calculated for each element which is included inside of the cone angle .theta. when viewed from the spotlight source. Thereafter, an intensity-value at each vertex of each element is calculated from the radiosity calculated for each element. Next, Gouraud shading is performed by using the intensity-value at each vertex of each element, and the result is displayed on a display.