PURPOSE: To enhance responsiveness in controlling the idling speed, by correcting the control speed of an idling-speed controlling apparatus according to the pressure in an intake pipe.

CONSTITUTION: An analogue signal proportional to the pressure in an intake pipe, detected by a pressure sensor 22, is converted into a digital value by an A/D converter 23 and furnished to an interface 24A of a micro-computor 24. The computor 24 calculates the constant of integration and constant of proportionality proportional to the pressure in the intake pipe by means of a micro-processor 24B and executes proportional plus integral control by use of the above control constants. By use of this control apparatus, the rate of change in the flow rate of by-pass air can be controlled to a constant value without influence of the change of the pressure in the intake pipe, and the actual engine speed Nr can be controlled to an aimed speed correctly. Thus, the response in controlling the engine speed can be enhanced.