PURPOSE: To facilitate generation of starting ignition pulses of all phases by only one digital processor by providing an initial control angle setting apparatus, a counter and a cross-reference table of the counted values for specific control angles and ignition arms.

CONSTITUTION: A counter 2 whose counted value is changed by one cycle during one cycle of an input voltage is prepared and set in such a manner that it starts down-counting or up-counting at the specific phase angle of the input voltage of a specific phase. A cross-reference table of the counted values of the counter 2 and the arms which is to be ignited at the specific control angles is prepared for each arm of all phases beforehand and stored in a memory 7. The output of an initial control angle setting apparatus 4 is given to a microprocessor 5 and the microprocessor 5 takes reference by shifting the counted value by a value corresponding to the difference between the control angle used when the cross-reference table is prepared and the control angle at which operation is actually started and selects the arm to be ignited and gives an ignition pulse to that arm.