Vehicle state observer system

A vehicle state observer system includes a state quantity measuring unit (21) which measures an observable quantity of state of a vehicle. A controlled variable detecting unit (22) detects a controlled variable of the vehicle. An observer (23) estimates an unobservable quantity of state of the vehicle from the observable quantity measured by the state quantity measuring unit and the controlled variable detected by the controlled variable detecting unit, in accordance with a system matrix including a system variable. A system variable detecting unit (24) detects the system variable included in the system matrix. A correcting unit (25) corrects a pole of the observer in response to the system variable detected by the system variable detecting unit.