A shaft-locking device which locks rotation of a movable shaft by a clamping force of a coil spring closely surrounding a fixed shaft and a movable shaft. Both sides of the coil spring are inserted surrounding the fixed shaft and a central portion of the coil spring surrounds the movable shaft. In case of rotation of the movable shaft on both sides, the locking torque is applied. Further, the closed state of the coil spring to the movable shaft is maintained uniformly without any relation to operation by separating the end portions of the coil spring at the movable shaft side of the coil spring from an outer circumference of the movable shaft so that a constant locking torque may be always obtained.