A driving position adjusting device comprises a seat-position adjusting mechanism to adjust height and seat-face angle of a seat cushion in accordance with longitudinal movement of a driver's seat, and a floor adjusting mechanism to adjust a height of a floor board in accordance with the operation of the longitudinal adjustment of the driver's seat, wherein the seat-position adjusting mechanism is configured so that an inclination angle of the seat cushion becomes smaller as the driver's seat is moved forward from a middle position, and the floor adjusting mechanism is configured so that the height of the floor board becomes higher as the driver's seat is moved forward from the middle position. Accordingly, the sitting position of the driver and the operational function of the operational pedal can be provided properly regardless of the body size of the driver.