An installation support unit includes a base board, a support member, two installation members and a locking member. An end board extends from the base board and has a bent portion. The support member has a face board and an elongate hole. Each of the installation members is connected to the support member which is fixed to the end board. The locking member is movably connected to the support member and the end board, and includes a head portion, a protrusion and a threaded hole defined through the head portion and the protrusion. The diameter of the protrusion is smaller than the transverse width of the elongate hole. The protrusion extends through the elongate hole, and the height of the head portion is longer than the longitudinal distance of the elongate hole. The head portion is movably clamped between the support member and the end board.