A connecting device adapted to connect a first wall to one of two second walls (20b, 200) of a furniture piece, the connecting device characterized by: a base portion connectable to the first wall of the furniture piece, wherein the base portion comprises a surface and a space adjacent to the surface; and an opening of the space is located at the surface, and at least one engaging arm (36, 36a, 36b) arranged at the base portion, the at least one engaging arm (36, 36a, 36b) being resiliently movable around a hypothetical axis, and the at least one engaging arm (36, 36a, 36b) being arranged with an engaging portion (46a, 46b), wherein the at least one engaging arm (36, 36a, 36b) is arranged inside the space, and a length of the at least one engaging arm (36, 36a, 36b) does not exceed the surface; an auxiliary portion substantially perpendicularly connected to the base portion, wherein the auxiliary portion comprises at least one fastening feature provided to be inserted by a fastening member. wherein the hypothetical axis is substantially parallel to the first wall when the device is connected to the furniture piece; wherein one of the second walls of the furniture piece is mountable to the engaging portion (46a, 46b) along a mounting direction via a mounting portion, arranged and adjacent to an end portion of the second wall upon connection and detachably mounted to the engaging portion (46a, 46b); wherein the mounting direction is substantially perpendicular to the hypothetical axis; wherein an end of the other second wall of the furniture piece is capable of abutting against the surface of the base portion, and the second wall of the furniture piece may be fixed to the auxiliary portion via the at least one fastening feature and the fastening member. a base portion connectable to the first wall of the furniture piece, wherein the base portion comprises a surface and a space adjacent to the surface; and an opening of the space is located at the surface, and at least one engaging arm (36, 36a, 36b) arranged at the base portion, the at least one engaging arm (36, 36a, 36b) being resiliently movable around a hypothetical axis, and the at least one engaging arm (36, 36a, 36b) being arranged with an engaging portion (46a, 46b), wherein the at least one engaging arm (36, 36a, 36b) is arranged inside the space, and a length of the at least one engaging arm (36, 36a, 36b) does not exceed the surface; an auxiliary portion substantially perpendicularly connected to the base portion, wherein the auxiliary portion comprises at least one fastening feature provided to be inserted by a fastening member. wherein the hypothetical axis is substantially parallel to the first wall when the device is connected to the furniture piece; wherein one of the second walls of the furniture piece is mountable to the engaging portion (46a, 46b) along a mounting direction via a mounting portion, arranged and adjacent to an end portion of the second wall upon connection and detachably mounted to the engaging portion (46a, 46b); wherein the mounting direction is substantially perpendicular to the hypothetical axis; wherein an end of the other second wall of the furniture piece is capable of abutting against the surface of the base portion, and the second wall of the furniture piece may be fixed to the auxiliary portion via the at least one fastening feature and the fastening member.