Herein disclosed is a seat sliding device which generally comprises a latch mechanism for latching a movable rail to a stationary and a walk-in mechanism for moving the seat forward when a seatback of the seat is inclined forward. The walk-in mechanism comprises a transmission member which cancels the latched engagement between the movable and stationary rails when turned in a given direction about an operation shaft of the latch mechanism, a memory lever pivotally supported by the transmission member and actable as a prop for keeping the transmission member in the latched engagment cancelling condition and a stepped elongate member fixed to the stationary rail and engageable with the memory lever in a manner to cancel the function of the prop when the seat is slided to a given position with the seatback inclined forward.