Priority can be calculated for works-in-process which are not in demand. A priority calculation device (110) comprises a priority calculation unit (124) which specifies a queue of lots in each production stage, a product category wherein the lot is to be used, and the number of components included in the lot, on the basis of information stored in a queue information storage area (115), and allocates priority for each lot so that when the specified lot is supplied to the production stage, a lot, by which a ratio of a component, in each product category, contained in a lot which is in a process subsequent to the process of the production stage is made closer to the ratio of demand in each product category specified by the information stored in a demand information storage area (113), is supplied into the production stage with higher priority.
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