PURPOSE: To adjust continuously an angle of elevation of a movable body by providing a clutch which is released only to a pull-up direction of the movable body, and providing a rotary friction part between the movable body or a fixed base, and the clutch.

CONSTITUTION: A ratchet 14 is provided on a friction plate 9, and a ratchet stopper spring 15 is engaged therewith. As for rotation of a friction plate shaft 10, it slips and rotates when a rotational force which is larger than a frictional force generated between the friction plate 9, and a plate spring 11 and a thrust receiving plate is applied to the friction plate shaft 10, but does not rotate since it does not slip, when said rotational force is small. In case when a shaft supporting movable body 2 is pushed by a hand, etc. in the direction as indicated with an arrow B, the shaft supporting movable body 2 can be moved to an optional position.