PURPOSE: To obtain a compact and simple appearance by a method in which the rotary flat face of a support arm and the rotary flat face of a connecting rod are almost matched at their central faces.

CONSTITUTION: The fitted parts of a door 1 with support arms 21 and 22 of hollow pipe are coupled by the first pivoted shaft Y in parallel with a shaft X. A connecting rod 22a having a long hole V in its partial portion is inserted into the arms 21 and 22 and one end of the rod 22a is pivotally attached to a pivotal support point Q on a fixed position in relation to the shaft X and coupled with the free end of a pendulum level L turnable in the flat face to the side boundary face. A projected shaft P turnable with the arms 21 and 22 set coaxially with the shaft X is thrust into the long hole V of the rod 22a and restrained so that the rod 22a always crosses at a fixed point to the arms 21 and 22. The other end of the lever 22a is in parallel with the first pivotal shaft V in relation to the door 1 but is pivotally coupled by different second pivotal shaft Z.