A visible device for the wall assembly of a structural element (69, 169) of a piece of furniture of the type comprising: a movable arm (34, 134) for the hooking of said device to a support fixed to the wall, the position of said arm (34, 134) with respect to said wall being regulated with respect to the height and depth by means of a first and second different regulation mechanisms (36, 37; 136, 137) respectively, said regulation mechanisms (36, 37; 136, 137) being fully contained inside a box-shaped body (31, 131), from a front side of which a hook-shaped end (39, 139) of said arm (34, 134) protrudes, said box-shaped body (31, 131) being composed of two half-shells (32, 33; 132, 133) which are firmly intercoupled by fixing means (66, 70, 71, 174, 174', 175), on the side (80,180) of said box-shaped body (31, 131), there also being respective access means (44, 64; 144, 164) to the side of said mechanisms (36, 37; 136, 137), and further fixing means (70, 172) to said component (69, 169), said first regulation mechanism (36, 136) comprising, in combination a screw (42, 142) which is screwed onto a sliding nut (43, 143) which acts on the end edge (45, 145) of a curved section (46, 146)), the head of the screw (42, 142) comprises a toothed crown (49, 149) with which a gear (50, 150) is engaged, rotating on a pin (51,151) whose rotation axis is perpendicular to that of the screw (42, 142), the pin (51, 151) is housed inside a hole (51', 151') of the half-shell (32, 132), a seat (52, 152) being situated in the gear (50, 150) for a manoeuvring tool passing through a hole (44, 144) of the half-shell (33, 133), the second regulation mechanism (37, 137) comprising, in combination: a screw (54, 154) which is screwed through a threaded hole (55, 155) of a pin (35, 135) on which the arm (34, 134) rotates, the translation of said screw (54, 154) being blocked at the rear end by a seat (57, 157) on which the screw (54, 154) itself is rotatingly assembled, whereas the head at the opposite end comprises a toothed crown (60, 160) whereby a gear (61, 161) is engaged, which can rotate on a pin (62, 162) whose rotation axis is perpendicular to that of the screw (54, 154), the pin (62, 162) is housed inside a hole (62', 162') of the half-shell (32, 132), a seat (63, 163) is situated in the gear (61, 161) for a manoeuvring tool passing through a hole (64, 164) of the half-shell (33, 133), characterized in that - the components (42, 142, 43, 143, 49, 149, 50, 150, 51, 151) of the above first control mechanism (36, 136), are housed inside a corresponding first seat (53, 153) defined by the coupling between the two half-shells (32, 132; 33, 133), the nut of the first mechanism being hexagonal and translating on guides provided on the same first seat, the curved section of the first mechanism sliding inside a corresponding slit (47, 147) of the body (31, 131), the end of said section (46, 146) opposite to (45, 145) being buffered against the branches (38, 138) of the hooking arm (34, 134) - the components of the above second regulation mechanism (37, 137) are housed inside a corresponding seat (65, 165) defined by the coupling between the two half-shells (32, 33; 132, 133), the translation of the screw (54,154) of the second mechanism being blocked at the front end by a support (56, 156), the front end (58, 158) of the screw (54, 154) being rotatingly housed inside a seat (59, 159) of the support (56, 156), said support having opposite ends which are housed inside corresponding slots provided on the same second seat,said first and second seat being separated each other. - the components (42, 142, 43, 143, 49, 149, 50, 150, 51, 151) of the above first control mechanism (36, 136), are housed inside a corresponding first seat (53, 153) defined by the coupling between the two half-shells (32, 132; 33, 133), the nut of the first mechanism being hexagonal and translating on guides provided on the same first seat, the curved section of the first mechanism sliding inside a corresponding slit (47, 147) of the body (31, 131), the end of said section (46, 146) opposite to (45, 145) being buffered against the branches (38, 138) of the hooking arm (34, 134) the nut of the first mechanism being hexagonal and translating on guides provided on the same first seat, the curved section of the first mechanism sliding inside a corresponding slit (47, 147) of the body (31, 131), the end of said section (46, 146) opposite to (45, 145) being buffered against the branches (38, 138) of the hooking arm (34, 134) - the components of the above second regulation mechanism (37, 137) are housed inside a corresponding seat (65, 165) defined by the coupling between the two half-shells (32, 33; 132, 133), the translation of the screw (54,154) of the second mechanism being blocked at the front end by a support (56, 156), the front end (58, 158) of the screw (54, 154) being rotatingly housed inside a seat (59, 159) of the support (56, 156), said support having opposite ends which are housed inside corresponding slots provided on the same second seat,said first and second seat being separated each other.