To provide a vehicle state amount estimating device capable of suppressing sudden change in behavior at the time of behavior control of the vehicle, in a vehicle state amount estimating device that estimates a target lateral acceleration used in a behavior control of a vehicle based on a lateral acceleration actual measurement value and a lateral acceleration estimated value at time of traveling of the vehicle; when estimating the target lateral acceleration based on the lateral acceleration actual measurement value and the lateral acceleration estimated value, the target lateral acceleration is estimated by performing weighting on the lateral acceleration actual measurement value and the lateral acceleration estimated value according to a state of side slipping of the vehicle.