To provide a seat for a vehicle with a more inexpensive hinge mechanism than a standard hinge mechanism.

The seat 1 has a back rest 4 connected with a seat body 2 through the hinge mechanism 5 with two cheek plates which can be fixed each other by means of a slag with teeth controlled by means of a cam. In order to fold forward the back rest 4, and then to return the back rest to the original position, the cam of the hinge mechanism 5 is cooperated with a restoring mechanism 9 constructed in a form of an independent assembly containing a driving part for itself connected with the cam by means of a mechanical connection containing a lost motion in which a driving member is not moved by movement of the cam but the cam is moved to its lock releasing position by the movement of the driving member.