SEATBELT RETRACTOR

A retractor includes a pretensioner unit (16), the pretensioner unit (16) including a pinion gear (165) configured to rotate in association with a windup drum, a piston (164) that causes the windup drum to rotate in a direction of winding webbing through the pinion gear (165), a cylinder (162) that holds the piston (164), and a gas generating member that fills an interior space (NS) of the cylinder with a gas to drive the piston (164). The cylinder (162) includes a gas release hole (625) on a side surface thereof, the gas release hole (625) being provided to be located: in an initial position of the piston (164) before gas generation, at a position at which the interior space (NS) and an outside thereof are not continuous with each other through the gas release hole (625); and after gas generation, at a position at which the interior space (NS) that has changed upon moving of the piston and the outside are continuous with each other through the gas release hole (625).