An object is to provide a cylinder device which can be used successfully over a long period of time. The cylinder device includes a cylinder, a piston, an external cylinder, a tank and first piping. The piston is slidably inserted into the cylinder. The piston divides an interior of the cylinder into a rod-side chamber and a piston-side chamber. The external cylinder is disposed outside the cylinder and covers the cylinder. The tank is formed in a space between the cylinder and the external cylinder and stores an operating fluid. The first piping constitutes part of a first passage through which passes the operating fluid supplied to and discharged from the rod-side chamber or the piston-side chamber. The first piping has two ends one of which has a larger outer diameter than the other end. The first piping is disposed in the tank.