To provide a shock absorber for a valve such as a check valve that prevents a water hammer phenomenon when a check valve installed in a pipeline of every type of plant or the like is closed, and enables quick opening and closing of a valve element.

The shock absorber for a valve has a cylinder body, a piston rod connected to a valve stem of a valve, and a piston, and resists a movement of the piston with fluid in the cylinder body. The inside diameter of the cylinder body 2 is gradually reduced in a movement direction of the piston 3 at valve closing. The piston 3 is formed when two semicircular platelike members 6 and 6a are turnably coupled with a hinge pin 8, and rotation stops are set to hold the platelike members 6 and 6a in a flat plate position at valve closing. The fluid resistance can increase with valve closing to prevent sudden valve closing and prevent a water hammer phenomenon. At valve opening, the piston 3 closes to reduce the fluid resistance and thereby ensure a quick valve opening action.