Hinging device (30) for a folding furnishing element, comprising a first supporting element (1) associated with a first component of the furnishing element and a second supporting element (2) associated with a second component of the furnishing element. The first supporting element (1) and the second supporting element (2) are hinged one with respect to the other. The hinging device (30) also comprises a cam (3) associated with the first supporting element (1) and able to selectively cooperate with the second supporting element (2) in order to determine the relative clamping of the two elements at least in a first position of use wherein they are substantially parallel.