Set-up reduction is an important aspect of the Japanese Just-In-Time (JIT) and Zero Inventory (ZI) concepts. In this paper, we first analyze the effects of set-up cost reduction on tatal inventory, average lot size and forecast horizon in the dynamic lot size model. We also examine the various effects of set-up cost reduction in the EOQ model and explain why many Japanese firms try to cut set-up cost and/or set-up time greatly.