CYLINDER DEVICE

The present invention provides a shock absorber serving as a cylinder device capable of securing a clearance between an outer tube and a peripheral member and improving bending rigidity of the outer tube. An outer tube housing an inner tube is provided with a pair of knuckle bracket fastening plates and protruding in one direction from an outer surface of the outer tube The pair of knuckle bracket fastening plates and has wide surfaces facing each other, and the wide surfaces are provided along an axial direction of the outer tube When the inside of a vehicle is defined as a virtual region I and the outside of the vehicle is defined as a virtual region II with a virtual line which passes through a stroke center line and matches the inside and outside of the vehicle, as a boundary in an orthogonal cross section at an arbitrary axial position of the outer tube orthogonal to the stroke center line of a piston rod a cross-sectional area Aof the outer tube in the virtual region I is made larger than a cross-sectional area Aof the outer tube in the virtual region II