Robots are increasingly performing human work as manufacturing is automated. Accordingly, the use of precision speed reducers has become essential for achieving precise control of the robot arm position. Curved tooth profiles, such as cycloid or involute tooth profiles, are generally used in precision speed reducers. Speed reducers with cycloid tooth profiles, which enable high precision control, are widely used to manipulate robot systems. This study proposes a speed reducer that has a trapezoidal tooth profile with straight lines. In this work, we mechanically analyzed trapezoidal tooth profiles, arid then measured performance was by various tests using a prototype manufactured specifically for this study.