A seatbelt retractor for use in a motor vehicle to retract a passenger restraining seatbelt to be fastened around an occupant. The seatbelt is wound around a rotatable takeup shaft in layers by a biasing force in the seatbelt retractor. Fixed on the takeup shaft is a ratchet wheel, and a pawl is opposed to the ratchet wheel, whereby when the pawl meshes with the ratchet wheel, and thereby stops the belt-unwinding rotation of the takeup shaft. An inertia lock mechanism is provided in the retractor to actuate the pawl to mesh with the ratchet wheel in a vehicular emergency situation. A cam mechanism is also provided in the retractor, which includes a cam member or ring rotated by the takeup shaft and a follower member or linear spring driven by the cam member and opposed to the pawl. The cam member actuates the follower member to move the pawl into engagement with the ratchet wheel when the seatbelt is unwound more than a predetermined value, namely a value necessary for the fastening of the seatbelt. When the seatbelt is unwound within the predetermined value from the takeup shaft, the takeup shaft is kept rotatable in either direction and its belt-unwinding rotation is stopped by the inertia lock mechanism during a vehicular emergency situation. When the seatbelt is unwound more than the predetermined value, the takeup shaft is automatically stopped in its belt-unwinding rotation by the cam mechanism.