To provide a spring device capable installable even in a narrow space.

The spring device is composed of: an outer cylinder 11 forming an opening 112 furnished with a fastening part 111 and having a coupling part 113; an inner cylinder 12 forming an opening 122 furnished with a fastening part 121 and having a coupling part 123; a rod 13 having a fastening part 133 and a sliding part 132; a sliding member 15 having a sliding hole 151; and a resilient piece 14 with the two ends secured by the sliding part 132 and the sliding member 15. The coupling parts 113 and 123 are coupled to the structure and a fixed end, respectively, and the inner cylinder 12 intrudes into and emerges from the outer cylinder 11 through the opening 122 while the rod 13 intrudes into and emerges from the outer 11 and inner cylinders 12. The sliding motion of the sliding member 15 in the axial direction within the outer cylinder 11 is restricted by the fastening part 111, and the relative displacement in the axial direction of the inner cylinder 12 and the rod 13 is restricted by putting the fastening parts 121 and 133 in fastening with each other.