A cylinder unit includes a cylinder, a rod guide, a piston, a piston rod, and a rebound member provided between the rod guide and the piston to absorb impact generated when the cylinder unit is fully extended. The rebound member includes a coil spring arranged around an outer circumference of the piston rod and a pair of upper and lower holder members fitted to the fixing portions formed in both ends of the coil spring so that the piston rod is inserted into a shaft center hole. The center portion formed between the fixing portions of the coil spring has a diameter smaller than that of the fixing portion.