In this paper, we analyze the inventory and inspect cost of small-to-medium-sized enterprises which are getting orders from large enterprises using JIT(just in time) system. So far, we have not found the good inventory and inspect cost formula for the small-to-medium-sized enterprises. In this paper, we first survey the inventory and inspect strategy and cost formula of the small-to-medium-sized enterprises in this country. We are trying to mathematical modelling of several cases depending on the inventory and inspect strategy of large enterprises. We suggest inventory and inspect several cost formula by using the method minimizing the total cost of the small-to-medium-sized enterprises. We also give some numerical examples for your understanding.