A three-dimensional measuring device includes a ball-shaped structure, an X-axis measuring module, a Y-axis measuring module and a Z-axis measuring module. The ball-shaped structure is moved and/or rotated in response to a movement of a movable object. The X-axis measuring module includes a first measuring structure and a first position sensor. The first measuring structure is movable along an X-axis direction and contacted with the ball-shaped structure. The Y-axis measuring module includes a second measuring structure and a second position sensor. The second measuring structure is movable along a Y-axis direction and contacted with the ball-shaped structure. The Z-axis measuring module includes a third measuring structure and a third position sensor. The third measuring structure is movable along a Z-axis direction and contacted with the ball-shaped structure.