A forced induction system comprising: a first forced induction device and a second forced induction device each including a turbine (32, 42) provided on an exhaust passage (51A, 51B, 52A, 52B, 53A, 53B) in an engine, the turbine (32, 42) including a turbine wheel (34, 44) configured to be actuated by exhaust air emitted from the engine, a variable nozzle mechanism (35, 45) configured to adjust an opening degree between adjacent nozzle vanes of a plurality of nozzle vanes disposed at an exhaust air entrance to the turbine wheel (34, 44), and a compressor (31, 41) provided on an intake passage (21, 22, 23, 37, 47, 27A, 27B) in the engine, the compressor (31, 41) being configured to compress air to be taken into the engine by actuation of the turbine (32, 42); and a control device configured to execute switching control for switching from a first forced induction mode to a second forced induction mode, the first forced induction mode being a mode in which air compressed in the first forced induction device is supplied to the engine, the second forced induction mode being a mode in which air compressed in the first forced induction device and air compressed in the second forced induction device join together to be supplied to the engine, characterized in that when the execution of the switching control is requested, the control device being configured to perform control so that a first opening degree of the variable nozzle mechanism in the first forced induction device is equal to a second opening degree of the variable nozzle mechanism in the second forced induction device, and execute an approach-run operation in which air compressed by the compressor of the second forced induction device is supplied to the compressor of the first forced induction device while exhaust air is supplied to the turbine of the second forced induction device, the control device being configured to switch to the second forced induction mode after a second boost pressure produced by the compressor of the second forced induction device reaches a first boost pressure produced by the compressor of the first forced induction device during the approach-run operation. a first forced induction device and a second forced induction device each including a turbine (32, 42) provided on an exhaust passage (51A, 51B, 52A, 52B, 53A, 53B) in an engine, the turbine (32, 42) including a turbine wheel (34, 44) configured to be actuated by exhaust air emitted from the engine, a variable nozzle mechanism (35, 45) configured to adjust an opening degree between adjacent nozzle vanes of a plurality of nozzle vanes disposed at an exhaust air entrance to the turbine wheel (34, 44), and a compressor (31, 41) provided on an intake passage (21, 22, 23, 37, 47, 27A, 27B) in the engine, the compressor (31, 41) being configured to compress air to be taken into the engine by actuation of the turbine (32, 42); and a turbine (32, 42) provided on an exhaust passage (51A, 51B, 52A, 52B, 53A, 53B) in an engine, the turbine (32, 42) including a turbine wheel (34, 44) configured to be actuated by exhaust air emitted from the engine, a variable nozzle mechanism (35, 45) configured to adjust an opening degree between adjacent nozzle vanes of a plurality of nozzle vanes disposed at an exhaust air entrance to the turbine wheel (34, 44), and a compressor (31, 41) provided on an intake passage (21, 22, 23, 37, 47, 27A, 27B) in the engine, the compressor (31, 41) being configured to compress air to be taken into the engine by actuation of the turbine (32, 42); and a control device configured to execute switching control for switching from a first forced induction mode to a second forced induction mode, the first forced induction mode being a mode in which air compressed in the first forced induction device is supplied to the engine, the second forced induction mode being a mode in which air compressed in the first forced induction device and air compressed in the second forced induction device join together to be supplied to the engine, characterized in that when the execution of the switching control is requested, the control device being configured to perform control so that a first opening degree of the variable nozzle mechanism in the first forced induction device is equal to a second opening degree of the variable nozzle mechanism in the second forced induction device, and execute an approach-run operation in which air compressed by the compressor of the second forced induction device is supplied to the compressor of the first forced induction device while exhaust air is supplied to the turbine of the second forced induction device, the control device being configured to switch to the second forced induction mode after a second boost pressure produced by the compressor of the second forced induction device reaches a first boost pressure produced by the compressor of the first forced induction device during the approach-run operation.