An end effecter is positioned with high precision by stabilizing its attitude. Included are arms each having a pair of rods arranged in parallel, a bracket having the end effecter attached thereto and retained by the pair of rods, ball joints and each including a first joint element having a ball and displaceably connecting the bracket with the arm and a second joint element having a socket for retaining the ball, a connecting member for connecting the pair of parallel rods together and restricting rotation of the rods about an axis that is parallel to the longitudinal direction thereof, and a biasing member for providing a biasing force for retaining the ball in the socket.