A latch device (20A) for latching an inclinable bark rest cushion (11) to a seatback (10) of a seat when the cushion is snugly received in a tunnel formed in the seatback (10). The latch device comprises a striker secured to the seatback (10), a latch member (30) pivotally mounted in the cushion (11), a spring (23) incorporated with the latch member (30) to bias the same in a direction to achieve a latched engagement between the latch member (30) and the striker (15), an actuation member pivotally mounted in the cushion (11) in a manner to push and pivot the latch member (30) in a releasing direction to cancel the latched engagement between the latch member (30) and the striker (15) when pivoted in a given direction, means having a pin portion which is projectable into a travelling way of the actuation member thereby to interrupt the actuation member from pivoting in the releasing direction, a base member (21) secured to a rigid portion of the cushion (11) and having an opening through which the pin portion passes, and a mechanism for manually actuating the pin portion from a back side of the back rest cushion (11).