An angle positioning device of a rotation shaft includes a first pivot portion and a second pivot portion. The first pivot portion includes a first face having a positioning portion, a first path and a second path divided by the positioning portion. The first pivot portion includes a second face having a returning portion, a third path and a fourth path divided by the returning portion. The second pivot portion can move along the first path, the second path, the third path, and the fourth path. When the second pivot portion moves from the first path to the second path, the pivot angle is increased. When the second pivot portion moves from the third path to the fourth path, the pivot angle is decreased. When the pivot portion moves from the first path to the positioning portion, the pivot angle cannot be decreased. The second pivot portion can move from the third path through the returning portion and back to the first path.