PURPOSE: To enable the determination of all lead angle characteristics through the combination of concrete values of parameter, by representing the firing timing lead angle characteristic with several proper parameters and associating the concrete values to each parameter.

CONSTITUTION: To obtain a lead angle characteristic to be determined by the distribution of the concrete values of three parameters and the selective specification of one concrete value from each parameter, by employing three parameters for the firing timing of the lead angle starting rotation R1, lead angle saturating rotation R2 and the saturating lead angle As. In other word, the rotation 13 is selected from a group of lead angle starting rotations 10 or the rotation 14 and the saturating lead angle 15 are selected from a group of lead angle saturating rotations 11 and a group of saturating lead angles 12 to determine the lead angle saturating point 16. Then desired firing lead angle characteristic 17 is determined from two points of said rotation 13 and the lead angle saturating point 16. The selection of such lead angle characteristic is performed by a microcomputer 18 including ROM28 for storing a data source corresponding to each parameter.