Abstract: An operation planning method is provided for making an operation plan for receiving a plurality of products from a supplier, and mounting at least one item on each of the products based on specifications of each product . In this method, information relating to the products received from the supplier is initially acquired. The products received is a mixture of products whose specifications are determined before transportation of the products from the supplier, and products whose specifications are not determined by the time of transportation of the products. Then, an order is placed for desired items to be mounted on the products whose specifications are determined before transportation thereof, and an order is placed for desired items to be mounted on products whose specifications are determined during transportation thereof.