Angular support device adapted to support a wall cabinet on a wall, said device comprising: - hooking means adapted to cooperate with engagement means wall-fixed to support the piece of furniture, and - a dihedral-shaped mounting body comprising a support plate whereon said hooking means can be mounted, and a mounting plate comprising a plate member defining an outer face which can be integrally constrained to the inner surface of the side of a piece of furniture, said support plate and said mounting plate being arranged, in use, on mutually perpendicular planes so as to define, in use, a rigid corner piece, said support plate and said mounting plate are made of respectively distinct and separate pieces, said mounting plate further comprising guide means to allow the sliding coupling with said support plate along a coupling direction (B, B') during assembly, wherein said guide means comprising - a pair of first guide fins projecting perpendicularly at corner portions of an inner face of said plate member of said mounting plate opposite to said outer face, - a pair of second guide fins projecting perpendicularly from said first guide fins, and - a pair of third guide fins either projecting perpendicularly from the ends of said first guide fins so as to form, together with the respective first and second guide fins (41, 42), a track for slidably inserting said support plate along a first coupling direction orthogonal to said plate member of said mounting plate, or projecting perpendicularly from the ends of said second guide fins, lying on a plane parallel to said plate member of said mounting plate so as to form, with the respective first guide fin, a guide for slidably inserting said support plate along a second coupling direction (B') parallel to said plate member of said mounting plate, said mounting plate further comprising retaining means moved from a neutral position to a retaining position during assembly for maintaining the assembly of said mounting body, preventing a backward sliding movement of said support plate. - hooking means adapted to cooperate with engagement means wall-fixed to support the piece of furniture, and - a dihedral-shaped mounting body comprising a support plate whereon said hooking means can be mounted, and a mounting plate comprising a plate member defining an outer face which can be integrally constrained to the inner surface of the side of a piece of furniture, said support plate and said mounting plate being arranged, in use, on mutually perpendicular planes so as to define, in use, a rigid corner piece, said support plate and said mounting plate are made of respectively distinct and separate pieces, said mounting plate further comprising guide means to allow the sliding coupling with said support plate along a coupling direction (B, B') during assembly, wherein said guide means comprising - a pair of first guide fins projecting perpendicularly at corner portions of an inner face of said plate member of said mounting plate opposite to said outer face, - a pair of second guide fins projecting perpendicularly from said first guide fins, and - a pair of third guide fins either projecting perpendicularly from the ends of said first guide fins so as to form, together with the respective first and second guide fins (41, 42), a track for slidably inserting said support plate along a first coupling direction orthogonal to said plate member of said mounting plate, or projecting perpendicularly from the ends of said second guide fins, lying on a plane parallel to said plate member of said mounting plate so as to form, with the respective first guide fin, a guide for slidably inserting said support plate along a second coupling direction (B') parallel to said plate member of said mounting plate, - a pair of first guide fins projecting perpendicularly at corner portions of an inner face of said plate member of said mounting plate opposite to said outer face, - a pair of second guide fins projecting perpendicularly from said first guide fins, and - a pair of third guide fins either projecting perpendicularly from the ends of said first guide fins so as to form, together with the respective first and second guide fins (41, 42), a track for slidably inserting said support plate along a first coupling direction orthogonal to said plate member of said mounting plate, or projecting perpendicularly from the ends of said second guide fins, lying on a plane parallel to said plate member of said mounting plate so as to form, with the respective first guide fin, a guide for slidably inserting said support plate along a second coupling direction (B') parallel to said plate member of said mounting plate, said mounting plate further comprising retaining means moved from a neutral position to a retaining position during assembly for maintaining the assembly of said mounting body, preventing a backward sliding movement of said support plate.