Abstract: A seat belt apparatus for an automobile includes a ratchet wheel and at least one pawl member for selectively braking a spool with respect to one direction of its rotation. The pawl member operates to perform the emergency locking and excessive-loosening preventing functions with respective to a belt. To precisely control the time for emergency stop of belt, the apparatus contains a fly wheel mass having a plurality of holes, and a web sensing spring one end of which is fixed to one of the holes. Further, to control the effective length of the belt, the apparatus includes cam protrusions, a cam gear and a cam plate which overlap to enable the distance control of the cam protrusions.