To provide a cylinder device, reduced in complicated component processing or complicated assembling operation.

The hydraulic cylinder 1a includes an outer cylinder 2 having an opening 4 at one end, a piston 14 slidably inserted into an inner cylinder 3 disposed within the outer cylinder 2 to divide the inside of the inner cylinder 3 to two chambers, a sealing member 6 inserted to the opening 4 of the outer cylinder 2 to seal the inside of the outer cylinder 2, an annular fixing member 10a inserted to the opening 4 of the outer cylinder 2 and disposed on the open side of the outer cylinder 2 relative to the sealing member 6, and a piston rod 15 inserted into the outer cylinder 2 through the sealing member 6 and the fixing member 10a and integrally moving with the piston 14. Since the fixing member 10a is caulked to the outer cylinder 2, mixing of fine chips by complicated component processing or the like into the outer cylinder 2 can be reduced to simplify the assembling operation.