Power transmission device that integrates a reduction gear with an AC motor, used in equipment requiring rotational speed control such as conveyor drives, mixers, pumps, and fans in manufacturing lines. It achieves high torque and low rotation that cannot be obtained with a motor alone, and is classified by reduction mechanisms such as parallel shaft, right-angle shaft, and planetary gear types. With a wide range of rated outputs from 0.1kW to several tens of kW, selection of mounting methods (flange, foot) and reduction ratios (1/3 to 1/3600) is important. Various application-specific specifications are available including inverter-compatible models, brake-equipped types, and waterproof specifications, provided as integrated complete units unlike separate AC motors or reduction gears.