CYLINDER DEVICE

The present invention provides a shock absorber serving as a cylinder device that makes it possible to ensure clearance between an outer cylinder and surrounding members, and to improve the flexural rigidity of the outer cylinder. Provided to an outer cylinder 104 accommodating an inner cylinder 103 are a pair of knuckle bracket fastening plates 110a, 110b that protrude out to one direction side from an outer surface of the outer cylinder 104. The pair of knuckle bracket fastening plates 110a, 110b are provided so as to have respective wide surfaces opposite each other, and so that the wide surfaces run along an axial direction of the outer cylinder 104. In an orthogonal cross-section at any location of the axial direction of the outer cylinder 104 orthogonal to a stroke centerline 71 of a piston rod 102, a cross-sectional area Ai1 of the outer cylinder 104 in an imaginary region I192 is greater than a cross-sectional area Ao1 of the outer cylinder 104 in an imaginary region II193, where the imaginary region