In a supercharger (10) with an electric motor in accordance with the present invention, the electric motor (20) is arranged at a position adjacent to a compressor impeller (6), a center housing (14) has a cooling fluid flow path (34) formed in such a manner as to surround the electric motor (20) and be adjacent to a diffuser portion (25). A first cooling structure portion (38) is formed at a position in the electric motor (20) side in the cooling fluid flow path (34), a second cooling structure portion (39) is formed at a position in the diffuser portion (25) side in the cooling fluid flow path (34). The electric motor (20) is cooled by the first cooling structure portion (38). The diffuser portion (25) is cooled by the second cooling structure portion (39).