A technique is provided that supports making evaluations of impact on a business performance indicator, which varies depending on timing at which a change of plan is decided. A sales plan evaluation support system, includes: a unit which obtains master information that includes a sales plan of a product and is used as input for material requirements planning (MRP) calculation; a first MRP calculating unit which obtains a first order-placement plan through MRP calculation by using the master information as input, the first order-placement plan including an ordered-item count and an order-placement date of a required item for the product; a revision timing setting unit which sets timing for revising the sales plan; a master modifying unit which modifies the master information; and a second MRP calculating unit which obtains a second order-placement plan through MRP calculation by using an order-placement plan having an order-placement date preceding the revision timing included in the first order-placement plan, as an order-placement plan which has been implemented prior to the revision timing, and by using, as input, master information modified by the master modifying unit, the second order-placement plan including an ordered-item count and an order-placement date of a required item for the product.