A cylinder device includes: a first piston (8) inserted in a first cylinder hole (4) so as to be movable in an axial direction, a piston rod (7) being hermetically inserted in the first piston (8), the first piston (8) being fixed to the piston rod (7); a second piston (10, 37) inserted in a second cylinder hole (5) so as to be movable in the axial direction, the piston rod (7) being inserted in the second piston (10, 37); and a partition wall (13) dividing a cylinder hole (6) into the first cylinder hole (4) and the second cylinder hole (5), the partition wall (13) being movable in the axial direction.