1. A simulation system for performing a practical simulation combining three-dimensional model of an operating machine such as a robot and a machine tool with three-dimensional model of a peripheral equipment or a workpiece, comprising: means for storing a three-dimensional model of the operating machine; drawing information input means for inputting drawing information representing at least one two-dimensional shape of the peripheral equipment or the workpiece, the drawing information including three-dimensional layout information for laying out the two-dimensional shape in a three-dimensional manner and operating-point information indicating a position at which the operating machine is operated; three-dimensional model generation means for assembling the three-dimensional model of the peripheral equipment or the workpiece by laying out the two-dimensional shape on a screen of the simulation system based on said three-dimensional layout information; and means for operating the three-dimensional model of the operating machine on said screen based on the operating-point information accepted from said drawing information.