A connecting device (1, 101, 201, 301) for an earthquake protection system, particularly for prefabricated panels, arranged to be positioned between a slab and a panel of a building, the connecting device comprising: - guide means; at least two sheet-like elements (2, 3, 102, 103), the two sheet-like elements (2, 3, 102, 103) being a lower element (2, 102) and an upper element (3, 103) mutually coupled; and at least one pair of plates (5', 5", 205', 205", 305', 305"), the two plates (5', 5", 205', 205", 305', 305") being a right plate (5', 205', 305') and a left plate (5", 205", 305") which can also be mutually coupled; said at least two sheet-like elements (2, 3) and said at least one pair of plates (5', 5", 205', 205", 305', 305") extending, in use, respectively, in a plane substantially parallel to the plane in which said slab lies and in a plane substantially normal to the plane in which said panel lies; and said at least two sheet-like elements (2, 3, 102, 103) and said at least one pair of plates (5', 5", 205', 205", 305', 305") having insertion means (2a, 3a, 102a, 103a, 5'a, 5'a, 205'a, 205"a, 305'a, 305"a) inside respective guide means (7, 8, 108, 207, 307); characterized in that said insertion means (2a, 3a, 102a, 103a) consist of a hook (2a, 102a) formed in the end portion of said lower element (2, 102) and a protrusion (3a, 103a) shaped in the form of an "S" on the end portion of said upper element (3, 103), in such a way that, in use, when said at least two sheet-like elements (2, 3, 102, 103) are moved towards each other during their engagement with said guide means (8, 108), the curved parts of said hook (2a, 102a) and of said protrusion (3a, 103a) are substantially coupled. - guide means; at least two sheet-like elements (2, 3, 102, 103), the two sheet-like elements (2, 3, 102, 103) being a lower element (2, 102) and an upper element (3, 103) mutually coupled; and at least one pair of plates (5', 5", 205', 205", 305', 305"), the two plates (5', 5", 205', 205", 305', 305") being a right plate (5', 205', 305') and a left plate (5", 205", 305") which can also be mutually coupled; said at least two sheet-like elements (2, 3) and said at least one pair of plates (5', 5", 205', 205", 305', 305") extending, in use, respectively, in a plane substantially parallel to the plane in which said slab lies and in a plane substantially normal to the plane in which said panel lies; and said at least two sheet-like elements (2, 3, 102, 103) and said at least one pair of plates (5', 5", 205', 205", 305', 305") having insertion means (2a, 3a, 102a, 103a, 5'a, 5'a, 205'a, 205"a, 305'a, 305"a) inside respective guide means (7, 8, 108, 207, 307); characterized in that said insertion means (2a, 3a, 102a, 103a) consist of a hook (2a, 102a) formed in the end portion of said lower element (2, 102) and a protrusion (3a, 103a) shaped in the form of an "S" on the end portion of said upper element (3, 103), in such a way that, in use, when said at least two sheet-like elements (2, 3, 102, 103) are moved towards each other during their engagement with said guide means (8, 108), the curved parts of said hook (2a, 102a) and of said protrusion (3a, 103a) are substantially coupled.