PURPOSE: To prevent unnecessary loosening of a seat belt by providing a means to prevent further retraction of the belt when a buckle is fastened and to memorize such condition for removal of tension on the belt returning it to such condition whenever the belt is pullel out.

CONSTITUTION: When the buckle is fastened a plunger 15 is pulled in due to the energizing of a solenoid 11 and a lever 16 and an arm 22 are turned counterclockwise engaging gears 19 and 20 to gears 8 and 9 respectively. When a shaft 5 and a dual gear 7 rotate in the pull in direction (clockwise) the gear 19 rotates faster than the gear 20 because of the larger gear ratio between the gear 9 and 20 than beween the gear 8 and 19 until a stopper 25 of the gear 19 comes in contact with a stopper 26 of the gear 20 stopping the rotation of the shaft 5 in the pull in direction as the two gears can not rotate relative to each other. When the belt is pulled out the shaft 5 and the gear 7 rotates counterclockwise separating the stoppers 25 and 26 but they return to the initial contact condition when the pull out force is removed.