A bracket device of a slide rail mechanism, comprising: an auxiliary supporting frame; and: a bracket mounted to the auxiliary supporting frame; an extension supporting frame movable relative to a rail member of the slide rail mechanism; and a reinforcing member connected to the extension supporting frame, wherein the auxiliary supporting frame is movable relative to the extension supporting frame; wherein one of the auxiliary supporting frame and the bracket comprises a first wall section and a second wall section, a space is defined between the first wall section and the second wall section, the bracket and the auxiliary supporting frame are movable relative to each other through the space; wherein the bracket comprises a first supporting protrusion located at one of an upper side and a lower side of the space for supporting the second supporting frame; wherein the auxiliary supporting frame comprises a front supporting protrusion located at the other one of the upper side and the lower side of the space for supporting the bracket; and wherein one of the extension supporting frame and the auxiliary supporting frame comprises an upper supporting wall, a lower supporting wall and a longitudinal wall connected between the upper supporting wall and the lower supporting wall, a passage is defined by the upper supporting wall, the lower supporting wall and the longitudinal wall, the upper supporting wall and the lower supporting wall are movable relative to each other through the passage, the extension supporting frame comprises a second supporting protrusion located at one of an upper side and a lower side of the passage for supporting the auxiliary supporting frame, the auxiliary supporting frame comprises a rear supporting protrusion located at the other one of the upper side and the lower side of the passage for supporting the extension supporting frame. a bracket mounted to the auxiliary supporting frame; an extension supporting frame movable relative to a rail member of the slide rail mechanism; and a reinforcing member connected to the extension supporting frame, wherein the auxiliary supporting frame is movable relative to the extension supporting frame; wherein one of the auxiliary supporting frame and the bracket comprises a first wall section and a second wall section, a space is defined between the first wall section and the second wall section, the bracket and the auxiliary supporting frame are movable relative to each other through the space; wherein the bracket comprises a first supporting protrusion located at one of an upper side and a lower side of the space for supporting the second supporting frame; wherein the auxiliary supporting frame comprises a front supporting protrusion located at the other one of the upper side and the lower side of the space for supporting the bracket; and wherein one of the extension supporting frame and the auxiliary supporting frame comprises an upper supporting wall, a lower supporting wall and a longitudinal wall connected between the upper supporting wall and the lower supporting wall, a passage is defined by the upper supporting wall, the lower supporting wall and the longitudinal wall, the upper supporting wall and the lower supporting wall are movable relative to each other through the passage, the extension supporting frame comprises a second supporting protrusion located at one of an upper side and a lower side of the passage for supporting the auxiliary supporting frame, the auxiliary supporting frame comprises a rear supporting protrusion located at the other one of the upper side and the lower side of the passage for supporting the extension supporting frame.