A cylinder device such as a power cylinder of a power steering system includes a slidable shaft slidably disposed inside a housing. A joint member is connected to the end section of the slidable shaft. A stopper member is disposed between the slidable shaft and the joint member. Here, the end section of the slidable shaft is cutout to form an axial engagement surface. The slidable shaft and the joint member are connected in a condition where the end face of the slidable shaft is in contact with the end face of the joint member so as to from a groove between the axial engagement surface and the joint member. The stopper member is formed annular and has an engagement section formed along its inner periphery. The engagement section is fitted in the groove so that the stopper member is prevented from at least an axial movement.