Abstract: An object of the present invention is to provide a ball plunger wherein a main ball of the ball plunger is rotated surely and smoothly, when a mold, jig or other article is fixed, positioned, or transported. Another object is to control and keep constant the main ball projection height from a surface fixed to the ball plunger. A plurality of the sub balls are accommodated on the bottom portion of the ball roller which farther accommodates the main ball on the sub balls, thereby reducing the rolling friction between the main ball and the sub balls. Thus, the main ball rolls smoothly. The ball roller and the spring is inserted into the casing. Finally, the spring is fixed to the casing by the coupling ring such as a c-shaped ring.