A latch device for a webbing anchor used in the seat belt system of a vehicle comprises a guide rail disposed in the vehicle with a predetermined locus, an anchor to which the end of webbing is fixed and which has an engaging pawl, the anchor being engaged with the guide rail for movement along the track of the guide rail, a driving member slidable along the guide rail and engaged with the anchor so as to be relatively displaced by a predetermined amount in the direction of sliding movement, the driving member being adapted to drive the anchor on the guide rail to bring the same to a seat occupant restraining position and a seat occupant non-restraining position, and a latch member fixedly disposed adjacent to the driving member and having an engaging portion engageable with the engaging pawl of the anchor and a cam portion forming cam means with the driving member.