A carrier for installation in a receiving space of a chassis includes a carrier body having a bottom wall and two sidewalls that cooperatively define a carrying space. The bottom wall has two opposite short sides respectively defining front and rear sides of the carrier body. A front shell is connected to the front side of the carrier body, and includes a front cover plate and two connecting walls extending into the carrying space and respectively and adjustably connected to the sidewalls in an overlapping manner to adjust a distance between the front cover plate and the rear side of the carrier body, so that the length of the carrier corresponds to the depth of the receiving space of the chassis.