Abstract: A cylinder device includes a cylinder head, a piston rod, a stroke detection unit that is provided in a housing chamber so as to open to a center hole of the cylinder head and outputs a detection signal corresponding to a stroke of the piston rod relative to the cylinder head, two bearing members that are installed along a longitudinal direction of the piston rod so as to sandwich the housing chamber in the center hole of the cylinder head, and a sealing system that is configured in a portion corresponding to a distal end side of the piston rod compared with the bearing members in the center hole of the cylinder head, and the piston rod is supported by the cylinder head via the two bearing members.