In assistance function evaluation apparatus and method for a vehicle dynamics control system, the vehicle dynamics control system being an object to be evaluated, a simulator is provided to obtain a data base when the vehicle dynamics control system is operated, a vehicle model, a road surface environment model, and a driver model that calculates a steering angle imposed on the vehicle model to trace a target course are provided, the simulator comprises a driver intention quantity detecting section that detects an intention quantity of a vehicle driver to move the vehicle in a lateral direction and a system function detecting section that detects a function quantity of the vehicle dynamics control system and evaluates that the assistance function of the vehicle dynamics control system is in conformity to the driver when the system function quantity and the driver intention quantity are balanced without excess or deficiency.