A position adjusting device, which adjusts the position of a seat in a height direction, includes a seat support plate that supports the seat and a rotary link that rotates integrally with the seat support plate when the position of the seat is adjusted. The seat support plate includes a front portion that is positioned directly under an occupant's buttocks when the occupant is seated in the seat, and a rear portion that is positioned on the rear side of the front portion. The rotary link includes a front link and a rear link that are provided at positions different from each other in a front to back direction. The front link and the rear link are mounted on the front portion, and the width of the front portion is smaller than the width of the rear portion.