The rear left attachment member 1100 and the rear right attachment member 1200 are then affixed to the rear side of the rack 10. In particular, the rear left attachment member 1100 and the rear right attachment member 1200 are connected to the rear wall 67 of the base 22 on the rear side of the rack 10. Alternatively, the rear left and rear right attachment members 1100, 1200 can be connected to the rack 10 before the rack 10 is lowered to be supported by the ground surface of the data center, a supporting component of the rack-supporting frame 102, or the upper end 19 of another rack 10. Once the rear left and rear right attachment members 1100, 1200 are connected to the rack 10, a part of each of the rear left attachment member 1100 and the rear right attachment member 1200 extends leftward and rightward respectively from a left end and a right end of the base 22 of the rack 10. Notably, in this embodiment, the hook portion 1110, the frame attachment portion 1120 and the spring portion 1130 of the rear left attachment member 1100 extend leftward from the left end of the base 22 of the rack 10, while the frame attachment portion 1220 and the spring portion 1230 of the rear right attachment member 1200 extend rightward from the right end of the base 22 of the rack 10. For instance, FIG. 11 shows the rear left and rear right attachment members 1100, 1200 connected to the rear side of the rack 10, with the left and right vertical support units 104 removed for clarity.