Necessary stock amount calculation system and medium having program stored therein

The invention provides a necessary inventory amount calculation system and a medium storing a program, which can calculate the necessary inventory amount of raw materials and the like with less man-hour and low cost. The calculation system is provided with: a finished product importance coefficient calculation unit that calculates a finished product importance coefficient; a procurement risk degree coefficient calculation unit that calculates a procurement risk degree coefficient for each raw material or semi-finished product; a comprehensive coefficient calculation unit that calculates a comprehensive coefficient on the basis of the product of the finished product importance coefficient and the purchase risk coefficient; a necessary inventory period calculation unit that calculates a necessary inventory period by multiplying each of the integrated coefficients by a preset longest inventory period, and sets the necessary inventory period as a period corresponding to a preset shortest inventory period when the