A cylinder device includes a piston rod that is inserted into a cylinder so as to be movable back and forth. The piston rod has a rod portion that extends outside the cylinder, and a piston connected to an end portion of the rod portion, the piston moving in the cylinder in a slidable manner. The rod portion has a rod inner space formed in the rod portion, the rod inner space communicating with the piston-side chamber of the cylinder, a first communicating passage that connects the rod inner space and the rod-side chamber of the cylinder, and an orifice plug provided in the first communicating passage in a changeable manner. The piston is connected to the rod portion so as to cover a part of the orifice plug.