Abstract: A decision support system collects and analyzes necessary information about an object on which a decision is to be made, and presents a plurality of alternative items to give support to making a decision. To efficiently and quickly perform the process repeatedly by making similar, not routine decisions, a case decided by an alternative item selecting unit is extracted by a case learning unit and stored by a case accumulating unit. When a decision is to be made on a new object, the accumulated similar past cases are extracted by comparing input object information by an object information comparing unit to give support to selecting an alternative item. Necessary information can be obtained through an interactive guide by a selection speeding up unit and the optimum alternative item is output by the software of the alternative item selecting unit.