A turbocharger comprising: a turbine wheel driven by exhaust gases exhausted from an internal combustion engine; a first compressor wheel and a second compressor wheel both coaxially connected to the turbine wheel through a shaft member; a main housing that accommodates therein the first and second compressor wheels (4, 5) and has a communicating passage defined inside of the main housing for sending air pressurized by the first compressor wheel to the second compressor wheel; an electric motor having a cylindrical motor housing and installed in the communicating passage and structured to share the shaft member common to the first and second compressor wheels (4, 5) and the turbine wheel as a rotation axis; a plurality of radiating fins (23, 24) provided between the main housing and the motor housing inside of the main housing and configured to partition the communicating passage into a plurality of regions in a circumferential direction; a control unit configured to control the electric motor; and a cooling mechanism structured to cool potential heat-generation portions inside of and outside of the main housing, wherein the cooling mechanism comprises: (i) a first cooling part placed in the radiating fins for cooling the air in the communicating passage by cooling water supplied to the first cooling part; (ii) a second cooling part placed in the motor housing for cooling a stator of the electric motor by cooling water supplied to the second cooling part; and (iii) a third cooling part having a cooling structure that cools the control unit by cooling water supplied to the third cooling part. a turbine wheel driven by exhaust gases exhausted from an internal combustion engine; a first compressor wheel and a second compressor wheel both coaxially connected to the turbine wheel through a shaft member; a main housing that accommodates therein the first and second compressor wheels (4, 5) and has a communicating passage defined inside of the main housing for sending air pressurized by the first compressor wheel to the second compressor wheel; an electric motor having a cylindrical motor housing and installed in the communicating passage and structured to share the shaft member common to the first and second compressor wheels (4, 5) and the turbine wheel as a rotation axis; a plurality of radiating fins (23, 24) provided between the main housing and the motor housing inside of the main housing and configured to partition the communicating passage into a plurality of regions in a circumferential direction; a control unit configured to control the electric motor; and a cooling mechanism structured to cool potential heat-generation portions inside of and outside of the main housing, wherein the cooling mechanism comprises: (i) a first cooling part placed in the radiating fins for cooling the air in the communicating passage by cooling water supplied to the first cooling part; (ii) a second cooling part placed in the motor housing for cooling a stator of the electric motor by cooling water supplied to the second cooling part; and (iii) a third cooling part having a cooling structure that cools the control unit by cooling water supplied to the third cooling part. (i) a first cooling part placed in the radiating fins for cooling the air in the communicating passage by cooling water supplied to the first cooling part; (ii) a second cooling part placed in the motor housing for cooling a stator of the electric motor by cooling water supplied to the second cooling part; and (iii) a third cooling part having a cooling structure that cools the control unit by cooling water supplied to the third cooling part.