Patent ID: 8403365

Claim:
A seatbelt retractor comprising: a housing; a take-up drum that is rotatably supported at the housing and urged in a webbing-take-up direction while a webbing is wound therearound; and a pretensioner mechanism that forces the take-up drum to rotate in the webbing-take-up direction in case of vehicle collision and takes up the webbing in the take-up drum, wherein the pretensioner mechanism comprises: a gas generating member that generates gas; a cylinder that is long and coupled with the gas generating member; a pinion gear body that is capable of rotating integrally with the take-up drum; a piston that is housed in the cylinder in a movable manner, pressed and driven by pressure of the gas, equipped with a rack getting engaged with the pinion gear body at a side surface portion thereof, and forced to rotate the take-up drum in the webbing-take-up direction via the pinion gear body when pressed and driven; and a sealing member that is a plate-like member having elasticity and a substantially similar shape with a gas-pressure-receiving-side surface of the piston, and mounted to the gas-pressure-receiving-side surface of the piston so as to seal a space between the piston and an inner wall of the cylinder, wherein the piston includes: a mounting concave portion having a predetermined depth at the gas-pressure-receiving-side surface thereof; and a communicating hole that is configured to perforate through the piston along a movement direction of the piston from the mounting concave portion, wherein the sealing member includes a mounting convex portion erected at a position that meets with the mounting concave portion, and wherein the sealing member is mounted to the piston with the mounting convex portion being press-fitted to the mounting concave portion, and configured so that the gas flows into the communicating hole from the mounting convex portion when the piston is pressed and driven by pressure of the gas.