A one-way clutch comprising: a first member arranged around a rotation axis, a second member arranged around the rotation axis so as to surround the first member, and a ratchet mechanism provided between the first member and the second member, the ratchet mechanism being configured to permit relative rotation between the first member and the second member in one direction, and the ratchet mechanism being configured to stop relative rotation between the first member and the second member in the other direction, the ratchet mechanism including a pawl provided on one of the first member and the second member, the pawl being configured to pivot toward the other of the first member and the second member, a spring provided between the pawl and the one of the first member and the second member, the spring being configured to press the pawl toward the other of the first member and the second member such that the pawl pivots toward the other of the first member and the second member, and a spring seat that supports the spring, the spring being connected to the one of the first member and the second member via the spring seat, the spring seat including a planar portion having a planar shape for receiving one end of the spring, and characterized in that the spring seat includes a pair of guide portions (32a, 32b) extending from the planar portion parallel in a direction in which the spring extends or contracts and contacting the one of the first member and the second member. a first member arranged around a rotation axis, a second member arranged around the rotation axis so as to surround the first member, and a ratchet mechanism provided between the first member and the second member, the ratchet mechanism being configured to permit relative rotation between the first member and the second member in one direction, and the ratchet mechanism being configured to stop relative rotation between the first member and the second member in the other direction, the ratchet mechanism including a pawl provided on one of the first member and the second member, the pawl being configured to pivot toward the other of the first member and the second member, a spring provided between the pawl and the one of the first member and the second member, the spring being configured to press the pawl toward the other of the first member and the second member such that the pawl pivots toward the other of the first member and the second member, and a spring seat that supports the spring, the spring being connected to the one of the first member and the second member via the spring seat, the spring seat including a planar portion having a planar shape for receiving one end of the spring, and characterized in that the spring seat includes a pair of guide portions (32a, 32b) extending from the planar portion parallel in a direction in which the spring extends or contracts and contacting the one of the first member and the second member. a pawl provided on one of the first member and the second member, the pawl being configured to pivot toward the other of the first member and the second member, a spring provided between the pawl and the one of the first member and the second member, the spring being configured to press the pawl toward the other of the first member and the second member such that the pawl pivots toward the other of the first member and the second member, and a spring seat that supports the spring, the spring being connected to the one of the first member and the second member via the spring seat, the spring seat including a planar portion having a planar shape for receiving one end of the spring, and characterized in that the spring seat includes a pair of guide portions (32a, 32b) extending from the planar portion parallel in a direction in which the spring extends or contracts and contacting the one of the first member and the second member.