To solve the problems that a folding metal fitting is used for foldably installing a shelf board to a kitchen furniture or a common furniture and foldably installing an auxiliary top board to the main top board of a table, and since a conventional metal fitting has a plurality of levers or a long lever, its appearance is bad and sometimes the finger is injured by being pinched between the levers during use.

In the folding metal fitting, an inclined long hole is drilled into a movable piece to be mounted on the shelf board or the auxiliary top board, and a lock part is formed in the lower part of the movable piece. A connection pin moving inside the long hole is erected, and a stopper to be locked to the lock piece is formed in a fixed piece to be mounted to the furniture. Accordingly, since the movable piece is movable and rotatable along a fixed distance in relation to the fixed piece, the folding meal fitting not only gives no possibility of pinching the finger, but also can maintain the shelf board or the auxiliary top board in a stable state when the shelf board or the auxiliary top board is used in a horizontal state.