PURPOSE: To sufficiently improve assigning by setting an aerial LSI, selecting two LSIs for all the LSIs including the aerial LSI, and replacing its functional element.

CONSTITUTION: LSIA-C are mounted at predetermined positions of a mounting board 11, a state that the LSIA-C are wire-connected is expressed as a data structure, aerial LSIA'-C, are disposed at the same positions of the LSIA-C, and they are added to the data structure. Two LSIs are selected at random from all the LSIs including the aerial LSIA'-C', one logic elements are selected at random, and replaced from each other. With the entire wire length between the LSIs before and after the replacement and the number of pins of the aerial LSIs as variables an evaluation function is calculated, discriminated by a discrimination formula, desirable one before and after the replacement is selected, and a state that the number of pins of the LSIA'-C' is zero and the entire wire length is as short as possible is obtained. Thus, the assignment of logic elements can be improved.