Abstract: In extracting parameters for use in circuit simulation of an IC device having a plurality of insulated gate field-effect transistors (IGFETs), layout data for patterns for the IC device are prepared. The patterns include gate patterns for the IGFETs, at least one of which is a bent gate pattern such that drain and source regions are defined on opposite sides of the bent gate pattern. An index symbol data is added to the layout data, which is for the bent gate pattern, to thereby form designed pattern data. For higher accuracy of the circuit simulation, the index symbol data in the designed pattern data is detected and used to produce parameters concerning the gate patterns for the IGFETs, thereby contributing to determination of a capability of controlling electric current in the IGFETs.