In a seat in which the seat is placed so as to be freely moved by a slide rail 4, a striker lock 7 retained and mounted to a striker 8 standing up from a vehicle body floor F is provided in a lower portion close to a rear end of a lower rail 4b, and the seat is placed so as to be freely kicked up from a rear portion side to an upper side in a folded state around a supporting shaft 6 axially supporting and pivoting a front end side of the lower rail 4b corresponding to a supporting point, there is provided a switching mechanism 10 which makes it impossible to unlock the striker lock 7 by an operation lever when the seat is kept at a front seated position, and makes it possible to lock the striker lock 7 by the operation lever when the seat is moved to a predetermined rear position, whereby it is possible to mechanically execute a step of moving the seat to the predetermined position in the rear side within the vehicle, thereafter unlocking the striker lock 7 and kicking up the seat.