Shipbuilding is an industry in which the change in demand has been extremely drastic. Therefore, it is important to develop a method of demand forecasting for new ships to realize sustainable development of the shipbuilding industry. In this paper, a system dynamics model for demand forecasting of ships is discussed. The target ship type is the bulk carrier, and the target cargo commodities are iron ore, coal, and grain. To express shipbuilding market characteristics, causal relations between economic growth, sea cargo movement, ship bottoms, ship orders, construction, and ship scrapping are examined, and the cargo transportation prediction model, order prediction model, construction model, and scrap model are defined. Thus, demand-forecasting simulations using the proposed model are conducted, and the effectiveness of the proposed model is shown.