To provide a 6-freedom-degree robot arm mechanism securing a wide action range by resolving a defect of having a small action range, while holding the rigidity, or an advantage of a parallel mechanism.

The conventional parallel mechanism is so formed that a movable member is supported by multiple connecting rods, the connecting rods are extended/contracted, and one end of the connecting rod is made to move relative to a base member. This parallel mechanism robot arm also moves one end of the connecting rod, however, the moving direction is made to same thereto so that based on a principle capable of moving in the direction theoretically infinitely, the action range can be set long. An actuator is disposed on the same base so that there is no obstacle in the vertical direction on the base surface, thereby setting the action range long in this direction.