The well-used actuators for the attitude control of spacecrafts are thruster, reaction wheel, control moment gyroscope, and magnetic torquer. Among them, the control moment gyroscope(CMG) which generates the torque based on the gyroscopic principle in physics, has an advantage of the high torque output compared to the low power consumption. This paper introduces an outline of CMG hardware technology, its application history in spacecrafts, and their associated hardware characteristics. Moreover, its spin-off cases to the other industrial fields such as ship, robotics, and MEMS including their research trend are provided.