PURPOSE: To make easy positioning by providing a first part capable of sliding around an axis of a support receiving the part, a second part capable of rotation by means of a joint around a shaft orthogonal to the former axis, and lock means on a single fixation axis on a side of any one of the parts.

CONSTITUTION: A central passage 12 is provided at a central portion of a U shaped support 10, a first articulation locking arm 20 is mounted, and a shaft 40 is fixed into openings 15, 16 of wing portions 13, 14. A shaft 31 orthogonal to a body 32 and a central passage 33 are provided to a second articulation locking arm 30, the shaft 40 is inserted into the passage 33 so as to be rotate, and the whole is locked at a required position by a fixing screw 50. Shoes 60, 70 having central openings 65, 75 for hollow portions 63, 73 fixing screw 50 corresponding to a head 22 of the arm 20 are disposed in the support 10. Accordingly, positioning fixing operation of the arms 20, 30 connecting the respective parts can be made easy.