Patent ID: 8167284

Claim:
A hook structure for a spiral spring, comprising: a first spiral spring; a second spiral spring that is smaller than the first spiral spring and is housed in an open space in a center of the first spiral spring; and a latch that is provided between the first spiral spring and the second spiral spring and to which an inner end of the first spiral spring and an outer end of the second spiral spring are hooked, wherein an inwardly-folded portion of the inner end of the first spiral spring is hooked to the latch under tension from an inner peripheral side of the first spiral spring while an outwardly-folded portion of the outer end of the second spiral spring is hooked in the latch under tension from an outer peripheral side of the second spiral spring, a receiving space is formed between an inner peripheral surface of an initial winding portion that starts winding in a curved shape from the folded portion of the inner end of the first spiral spring and an outer surface of the latch that faces the inner peripheral surface, and when the outer end of the second spiral spring is hooked in the latch from the outer peripheral surface, a tip of the folded portion of the outer end that projects to an outer surface side of the latch is housed in the receiving space.