A supercharger system for an internal combustion engine, comprising: a first supercharger; and a second supercharger, wherein the first supercharger includes a first compressor wheel arranged in an intake passage of the internal combustion engine, a first turbine wheel arranged in an exhaust passage of the internal combustion engine and coupled by a first shaft to the first compressor wheel, a first compressor housing accommodating the first compressor wheel, and a first turbine housing accommodating the first turbine wheel; the second supercharger includes a second compressor wheel arranged in the intake passage, a second turbine wheel arranged in the exhaust passage and coupled by a second shaft to the second compressor wheel, a second compressor housing accommodating the second compressor wheel, and a second turbine housing accommodating the second turbine wheel; the first and second compressor housings (51, 52) and the first and second turbine housings (61, 62) are configured so that at least either one of part of the second compressor housing and part of the second turbine housing is located in a space formed between the first compressor housing and the first turbine housing; and the first compressor wheel is larger in size in a radial direction than the second compressor wheel, and the first turbine wheel is larger in size in the radial direction than the second turbine wheel; the supercharger system being characterized in that the second turbine housing accommodates a variable flow rate mechanism that can vary a flow rate of exhaust acting on the second turbine wheel, the variable flow rate mechanism including a cylinder valve that moves along an axial direction of the second shaft; and the cylinder valve being configured so that most of the exhaust flowing into the second turbine housing is acting on the second turbine wheel when flowing out of the second turbine housing, if the cylinder valve is at a fully-closed position, and that most of the exhaust flowing into the second turbine housing is not acting on the second turbine wheel when flowing out of the second turbine housing, if the cylinder valve is at a fully-open position. a first supercharger; and a second supercharger, wherein the first supercharger includes a first compressor wheel arranged in an intake passage of the internal combustion engine, a first turbine wheel arranged in an exhaust passage of the internal combustion engine and coupled by a first shaft to the first compressor wheel, a first compressor housing accommodating the first compressor wheel, and a first turbine housing accommodating the first turbine wheel; the second supercharger includes a second compressor wheel arranged in the intake passage, a second turbine wheel arranged in the exhaust passage and coupled by a second shaft to the second compressor wheel, a second compressor housing accommodating the second compressor wheel, and a second turbine housing accommodating the second turbine wheel; the first and second compressor housings (51, 52) and the first and second turbine housings (61, 62) are configured so that at least either one of part of the second compressor housing and part of the second turbine housing is located in a space formed between the first compressor housing and the first turbine housing; and the first compressor wheel is larger in size in a radial direction than the second compressor wheel, and the first turbine wheel is larger in size in the radial direction than the second turbine wheel; the supercharger system being characterized in that the second turbine housing accommodates a variable flow rate mechanism that can vary a flow rate of exhaust acting on the second turbine wheel, the variable flow rate mechanism including a cylinder valve that moves along an axial direction of the second shaft; and the cylinder valve being configured so that most of the exhaust flowing into the second turbine housing is acting on the second turbine wheel when flowing out of the second turbine housing, if the cylinder valve is at a fully-closed position, and that most of the exhaust flowing into the second turbine housing is not acting on the second turbine wheel when flowing out of the second turbine housing, if the cylinder valve is at a fully-open position.