Opening apparatus separably mountable with a waste container which comprises a containment chamber, said opening apparatus is adapted to pass from a closing position which does not provide accessible openings to said containment chamber to an opening position which provides at least an access opening to the containment chamber, said opening apparatus comprising a coupling body couplable with said container, said opening apparatus comprising a drawer rotatably mounted with said coupling body defining a first rotation axis of said drawer, said drawer and said coupling body defining a chamber of predefined volume for housing a waste bag of said predefined volume, the opening position of said opening apparatus provides that said drawer is in an opening angular position wherein said waste bag can be inserted through said chamber of predefined volume, said opening apparatus passing from the opening position to the closing position provides that said drawer rotates about the first rotation axis closing the chamber directed towards the outside of the container and directing the opening of the chamber of predefined volume towards the inside of the containment chamber, the closing position of the opening apparatus provides that the drawer is in the closing angular position completely closing the chamber of predefined volume towards the outside of the container and opening it to its utmost extent towards the inside of the containment chamber, wherein said drawer has a solid dihedral geometrical shape and comprises a transverse section with circular-sector shape which comprises two radial walls (31, 32), a front wall and a rear wall, protruding along two different radial directions with respect to the first rotation axis of the drawer defining an angle (θ) measured on a geometric plane perpendicular to the first rotation axis, where said angle (θ) is predefined according to the predefined volume of the chamber, wherein said opening apparatus comprises a tilting wall, at least a guide element and at least a spacing bar, said tilting wall is hinged at a point of the coupling body and defines a second rotation axis, said at least one guide element is hinged at another point of the coupling body and defines another rotation axis, wherein the first, the second and the other rotation axis are parallel, said tilting wall rotates about said second rotation axis bonded by said at least one spacing bar which comprises an upper end hinged with another point of said at least one guide element and a lower end hinged at a point of said tilting wall, said tilting wall is adapted to pass from a closing position of an access opening of said chamber of predefined volume to an opening position of said access opening of said chamber of predefined volume which corresponds to the closing position of said opening apparatus, wherein said drawer comprises at least one engagement means (36, 37) slidably engaged with at least one guide slot of said at least one guide element, where said at least one guide slot (26, 28) comprises an upper stop portion and a lower stop portion, wherein at least one engagement means (36, 37) of the drawer in one of the abutment positions against the two respective stops of said at least one guide slot (26, 28) drags said at least one guide element rotating said guide element about the other rotation axis, wherein said at least one guide slot (26, 28) of said at least one guide element has a curvilinear shape comprising variable radii of curvature according to angular positions of the drawer so that said tilting wall passes from the opening position into the closing position of the opening apparatus. wherein said drawer comprises at least one engagement means (36, 37) slidably engaged with at least one guide slot of said at least one guide element, where said at least one guide slot (26, 28) comprises an upper stop portion and a lower stop portion, wherein at least one engagement means (36, 37) of the drawer in one of the abutment positions against the two respective stops of said at least one guide slot (26, 28) drags said at least one guide element rotating said guide element about the other rotation axis, wherein said at least one guide slot (26, 28) of said at least one guide element has a curvilinear shape comprising variable radii of curvature according to angular positions of the drawer so that said tilting wall passes from the opening position into the closing position of the opening apparatus.