A safety apparatus of a seat for a vehicle with a height adjustment device may include a height link that has one end rotatably connected to a seat rail bracket and the other end fixed to a rear hinge pipe, a restriction link that may be disposed at a side of the height link and has one end pivotally coupled to the seat rail bracket, wherein the restriction link may be elastically biased away from the height link, a first anti-rotation mechanism that may be disposed at the height link and the restriction link to restrict rotation of the height link when a front of the height link rotates upward in a front collision, and a second anti-rotation mechanism that may be disposed at the height link and the restriction link to restrict rotation of the height link when a rear of the height link rotates upward in a rear collision.