INTERNAL COMBUSTION ENGINE SYSTEM

An internal combustion engine system (10) includes: an electric supercharger (26) and a turbo-compressor (20a) that are arranged in series in that order; a first intake bypass passage (22) that bypasses the turbo-compressor (20a); and a first intake bypass valve (24) that opens and closes the first intake bypass passage (22). In a case where a request to decelerate the internal combustion engine is issued during driving of the compressor wheel (26a) by the electric motor (26b), driving of the compressor wheel (26a) by the electric motor (26b) is stopped simultaneously with the start of an opening operation by the first intake bypass valve (24).