A motion state estimation apparatus for a vehicle estimates the state of turning on the basis of the fact that changes in the tire pressures of the right-hand wheels and changes in the tire pressures of the left-hand wheels can serve as values which accurately represent the magnitude and direction of a lateral acceleration of the vehicle. The apparatus also estimates the state of acceleration in the fore-aft direction on the basis of the fact that changes in the tire pressures of the front wheels and changes in the tire pressures of the rear wheels can serve as values which accurately represent the magnitude and direction of a fore-aft acceleration of the vehicle. Accordingly, the state of acceleration of the vehicle (accordingly, the motion state of the vehicle) can be accurately estimated without use of expensive acceleration sensors.