In the pretensioner, a guiding wall is provided in a generator-side passing portion of a gas passing portion, and an inner portion of the generator-side passing portion at a portion where the guard wall is set is located to a base end rather than a tip end of a wire protective cylinder. Further, a gas generator mounting hole and the generator-side passing portion is inclined to be directed the base end of the wire protective cylinder. For this reason, gas that is jetted from a gas generator is blown to the base end of the wire protective cylinder or a surrounding portion thereof. As a result, even though the thickness of the wire protective cylinder is not set to be large, it can be against pressure of the blown gas.