A distal side link hub is connected with a proximal end side link hub through three sets of link mechanisms for alteration in posture. At least two sets of the link mechanisms include an actuator for arbitrarily changing the posture of the distal end side link hub relative to the proximal end side link hub by rotating a proximal side end link member and a reduction gear unit for reducing the speed of and transmitting the operation amount of the actuator to the proximal side end link member. The reduction gear unit includes a geared speed reducing section having a small gear rotated by the actuator and a large gear provided in the proximal side end link member. The radius of pitch circle of the large gear is chosen to be equal to or greater than the arm length of the proximal side end link member.