PURPOSE: To provide a reverse rotation preventive spring in a machine constituting structure, with which good reliability is held even though a concentrated torque is applied to the part where the spring begins coiling.

CONSTITUTION: If a reverse rotation preventive spring A is embodied in the form of a coil spring, the part 4 where coiling begins encounters friction and wear. Therefore, the part 4 is provided with a projection 1 or recess so that the whole coil part 5 receives the torque, and thereby the part 4 is prevented from abnormal wear. This secures the reverse rotation preventive spring A for use in a machine constituting structure with an enhanced reliability.