Abstract: When an operator inputs a unit retrieval condition and a logic symbol, a condition input section stores them in a condition storage section. A condition display section displays them alternately one after another on a display device. When the operator inputs specific information for specifying the logic symbol among the displayed logic symbols for which a priority-given retrieval based on the unit retrieval conditions displayed ahead and behind the logic symbol should be performed, a condition operating section raises the priority order of the logic symbol in the condition storage section in accordance with the specific information. The condition display section performs a specific distinguishing display on the logic symbol, indicated by the accepted specific information, and the unit retrieval conditions displayed ahead and behind the logic symbol to distinguish them from other unit retrieval conditions and logic symbols.