In a two-stage supercharging electric-assist turbocharger, a first compressor wheel, a rotor of an electric motor, a second compressor wheel, and a turbine wheel are coaxially coupled to a same, common shaft member, in that order. A compressor housing is structured to define therein a communicating passage to accommodate the electric motor in the communicating passage. A first water jacket is formed in at least one rib integrally formed with an outer periphery of a motor housing and also serving as a radiating fin, for forced-cooling air flowing through the communicating passage. A second water jacket is formed in a motor housing for forced-cooling a stator of the electric motor. A third water jacket is formed in an intermediate housing constructing a part of the compressor housing for forced-cooling a control unit configured to control the electric motor.