PURPOSE: To obtain smooth controllability when an idling revolution number is properly set according to a load change by opening/closing selectively a plurality of ISCVs(idling speed control valves), by conducting opening control by means of the 1st ISCV, and arranging so that the 2nd ISCV may be made to conduct the control action of opening/closing alone.

CONSTITUTION: At what is provided with the 1st, 2nd ISCVs that are in parallel with each other, at an air bypass passage bypassing a throttle valve, the 1st ISCV setting opening calculating means M11 that calculates the setting opening of the 1st ISCV on the basis of a difference between an engine revolution number and a target idling revolution number, is provided. Also, the 2nd ISCV opening/closing setting means M12 controlling the 2nd ISCV, is provided. And comparison is made between the 1st ISCV setting opening and opening upper and lower limit values, by means of the setting means M12, and when the ISCV setting opening surpasses the opening upper limit value, the 2nd ISCV is opened, and when the 1st ISCV setting opening is lower than the opening lower limit value, control is made so as to close the 2nd ISCV.