Recently, product-reliability and process-reliability in product development processes has been regarded as an important issue in many manufacturers. TRIZ which is theory for inventive solving is required to obtain reliability of each process. To solve the technological problems, TRIZ provides problems can be occurred in product development processes as a contradiction matrix based on 40 creative invention principles with alternatives for physical and technological contradiction. This paper suggests the method for inventive solving to ensure the reliability assurance of product development processes based on TRIZ.