Abstract: Arm device adapted to move and position a first basic part (6) relatively to a second basic part (4), comprising at least three arms (1,2,3,7) capable of being extended and shortened in a controlled manner, said arms being free to pivot in attachments (5) on the second basic part, while one attachment on the first basic part is rigid, and one of said arms is torisonally rigid. A third basic part (15) is connected to the first basic part through a joint (16), and at least one auxiliary arm (12,13) is at one end connected to one of the arms (7) through a joint, while the other end of the auxiliary arm is connected to the third basic part (15), and the lengths of the auxilary arm can be varied. Thereby is achieved that the arm device has a large number of degrees of freedom with respect to movement of the third basic part, which holds a tool or a tool holder. Moreover, the tool or the tool holder may be journalled for rotation relatively to the third basic part ( 15).