A shock absorber is attached coaxially with a reciprocating rod driven by a reciprocating unit to prevent a bending moment from being applied to the reciprocating rod in absorbing an impact force. The shock absorber has a hollow rod provided with a through hole and an outer cylindrical body mounted outside the hollow rod so as to be movable axially relatively and attached to the reciprocating unit. An accommodating space is formed between the hollow rod and the outer cylindrical body. A spring force in a direction of being relatively directed to one end portion side of the hollow rod is applied to the outer cylindrical body by a compression coil spring. An annular piston for partitioning an accommodating space into two liquid chambers is provided in the hollow rod. When the impact force is applied to the hollow rod so as to be slid to the hollow rod, the liquid flows from one liquid chamber to another liquid chamber through a gap, whereby a resistance force is applied to the annular piston.