While a base model has been determined for a product, in a system for performing a configuration designing operation of the product by setting a specification value to a specification item of the product, a product configuration design aiding system aids that a configuration designer can easily perform the configuration designing operation while following a restriction condition of a specification value of a specification item. A specification configuration information database is constructed which describes restriction conditions available for the specification values with respect to the specification item, and a configuration designing screen for inputting the specification values with respect to the specification item is displayed so as to conduct an input by the configuration designer.