This paper deals with a problem to develop an effective production ordering system for reducing amplifications of production and inventory levels under some conditions of forecasting error and downtime In this paper, two types of production ordering systems are proposed. One is the rodering system which feedbacks the difference between rodered and produced quantities sensored at only inventory stage. The other in the rodering system which feedacks that difference sensored at both production and inventory stages. As a result, the relations among forecasting error, downtime and production and inventory levels are clarified as structural formula. Also, some numerical examples show that the productin ordering system which feedbacks that difference sensored at both production and inventory stages can reduce the amplification of inventory level without increasing the amplification of production level.