A spring type one-way clutch includes an outer ring rotatable about a rotary shaft and having an inner tubular portion, and a clutch spring mounted in the outer ring. The clutch spring includes a large-diameter coil spring portion, a transition portion connected to the winding end of the large-diameter coil spring portion, and a small-diameter coil spring portion connected to the radially inner end of the transition portion and wound in the opposite direction from the large-diameter coil spring portion. When the outer ring is rotated in the direction opposite the winding direction of the large-diameter coil spring portion, the large- and small-diameter coil spring portions are radially compressed and pressed against the inner tubular portion and the rotary shaft, allowing the rotary shaft to rotate together with the outer ring. The transition portion spirals radially inwardly in the winding direction of the large-diameter coil spring portion.