In a production planning system, the explosion of a product to parts is performed by a specification check device and a design passage judgement device. An MRP calculation control device, a leadtime forecasting device, an MRP explosion calculation device, a work load calculation device and a data input/output device cooperate to estimate a shop load and to calculate a leadtime with a work load and a production capacity taken into consideration, thereby drawing up a production plan. A problem area analysis device analyzes a problematical area in the production plan to display it by graphics of the data input/output device. Various adjustment devices carry out the adjustment of the production plan through a graphic interface.