A spinal fixation and retrieval device comprises a retrieval main body, two side pieces, and a fastening device for fastening substantially symmetrically the two side pieces with two sides of the retrieval main body. When the bicycle is folded, the front and rear wheels are located separately, each at one side of the beam and within the concave section of the S-shaped beam, so that the bicycle is more compact and has a less width after being folded. The second economizer circuit is connected to the second compressor.