A control system for a supercharged internal combustion engine provided with a main exhaust passage ( 20 ) extending through a turbocharger turbine ( 21 ) and further through a catalyst ( 23, 24 ) to open to the outside air, an exhaust bypass passage ( 25 ) by passing the turbocharger turbine by branching from the main exhaust passage at the upstream side of the turbine and merging with the main exhaust passage before reaching the catalyst at the turbine downstream side, and an exhaust bypass valve ( 26 ) provided at the exhaust bypass passage, the control system for a supercharged internal combustion engine controlling the ignition timing in accordance with at least one of the engine warmup state and the catalyst warmup state until warmup of the internal combustion engine and warmup of the catalyst are completed and further controlling the opening degree of the exhaust bypass valve based on the control of the ignition timing, is provided.