An electric motor tool is provided to simplify a structure and improve production and assembly efficiencies by forming a fixing plate which prevents reverse transmission of power of a motor in a symmetrical shape. In an electric motor tool(1), a drive motor(3) is installed on one side of a body(2). A transmission part(4) changes speed of a driving force from the motor. A chuck(6) couples a working tool(5) by using power generated from the transmission part. The transmission part has a power reverse transmission preventing unit which prevents reverse transmission of power of the motor and the transmission part caused by reverse transmission of power from the chuck.
