An apparatus for changing positions of a seat for vehicles includes mechanisms for adjusting the height of the seat for vehicles, adjusting reclining of the seat for vehicles, changing the seat for vehicles into a knee rest posture and changing the seat for vehicles into a relaxed comfort are integrated into one structure. Accordingly, a user selectively implements adjustment of the height of the seat for vehicles, adjustment of reclining of the seat for vehicles, change into the knee rest posture, and change into the relaxed comfort posture, etc., through operation of the switch.