A bracket of a cylinder device includes: a tubular portion having a C-shaped cross section, holding an outer periphery of the outer shell, and having a slit in a front portion; and a pair of mounting portions and protruding outward in the radial direction from both ends of the tubular portion in the circumferential direction. The tubular portion includes a hole formed to permit insertion of the protrusion, from at least one side portion to the back portion of the tubular portion.