To provide a lock mechanism for a seat track having superior space efficiency, capable of reducing the size and having superior strength.

The seat track is provided with a lower rail, an upper rail movably engaged with the lower rail and the lock mechanism for regulating the movement of the upper rail with respect to the lower rail. The lock mechanism comprises through-holes formed on side walls of the upper rail; a plurality of lock holes formed on the lower rail opposing to the through-holes of the upper rail; a lifting/lowering shaft vertically movably supported inside the upper rail; tilting lock members relatively rotatably supported by the lifting/lowering shaft, tilted to change the projected length in the horizontal direction along with the vertical movement of the lifting/lowering shaft and passing through the through-holes to be engaged with/disengaged from the lock holes; and a lock energizing member for energizing the tilting lock members in the direction of the lock position engaged with the lock holes.