PURPOSE: To change the selection reference for an instance used for resource estimation by estimating required resources and supporting the change of the selection reference for the instances.

CONSTITUTION: Selected and corrected pictures of the instance are displayed on a CRT 1 one by one. A resource estimation system selecting part 15 displays a resource estimation system selecting picture, and a user refers to this picture to select elements which determine the number of cables. A resource quantity calculating part 16 estimates the number of cables to be used for the purpose of a new development plant in this plant in accordance with cable number determining elements and the estimation system, which are selected on the resource estimation system selecting picture, and adds this estimated number to the sum total of the already estimated number of cables. Consequently, the user can easily select the cable use instance of a preceding plant to be used for estimation of the number of cables of the new development plant. Since the estimation method is selected also, the resource quantity is finely estimated in accordance with the variety of specifications of the new development plant.