A seat having a collision stopper (51) activated in a short time period in collision. The seat is constituted of a supporting link (23), a stopper link (55), a recess/ridge surface (61), a stopper (65), and urging means (67). The supporting link (23) is installed at its upper portion to the floor side and at its lower portion to the seat cushion side, supporting a seat cushion, and adjusts the height of the seat cushion by inclination in the forward and backward directions in the vertical plane. The stopper link (55) is attached at its base end section to the floor side such that a rotation end section is rotatable in the forward and backward directions in a vertical plane. The stopper link (55) has, on its rotation end section side, a projection (57) projecting sideward. The recess/ridge surface (61) is provided on the supporting link (23) side, extending in the direction intersecting the movement path of the projection. When engages with the projection upon receiving a collision load in an assumed direction, the recess/ridge surface (61) inhibits further rotation of the supporting link (23) by cooperating with the projection. The stopper (65) comes in contact with the projection at a position where the projection does not engages the recess/ridge surface (61), inhibiting the projection from further separating from the recess/ridge surface (61). The urging means (67) urges the stopper link (55) in the direction where the projection is in contact with the stopper.