To design a new logic circuit by utilizing an existent logic circuit.

The circuit constitution of a programmable logic circuit(PLD) is updated according to genetic algorithm to design a logic circuit which performs target output. According to the genetic algorithm, a set of rules for deriving BDT(binary decision tree) corresponding to the circuit constitution of the PLD is regarded as a chromosome (set of rules for deriving BDT), which is updated to derive a chromosome which provides optimum circuit constitution. When the existent logic circuit is utilized for circuit designing, the logic circuit and BDT are in 1:1 relation, so the existent logic circuit is converted into BDT, which can easily be built in a newly designed logic circuit.