An air supply control system for an internal combustion engine comprises a supercharging device operative to perform selectively a first supercharging operation by which supercharging efficiently under a first condition wherein the engine operates with relatively small intake air flow is improved and a second supercharging operation by which supercharging efficiency under a second condition wherein the engine operates with relatively large intake air flow is improved, an operation detector for detecting engine operations, a traveling condition detector for detecting traveling conditions to a vehicle equipped with the engine, a supercharging operation controller operative to cause the supercharging device to perform the first supercharging operation when a first engine operation attended with relatively small intake air flow is detected by the operation detector and to perform the second supercharging operation when a second engine operation attended with relatively large intake air flow is detected by the operation detector, and an operating area changer operative to vary, in accordance with traveling conditions detected by the traveling condition detector, a boundary between first and second operating areas provided on an operating characteristic chart of the engine for defining the first and second engine operations, respectively.