A motion state determination apparatus according to the present disclosure includes a sensor for obtaining observation data on a target object, a route data storage unit, a route component predictor that calculates component parallel and vertical to the route of a motion-dimension prediction value and a prediction error, a first coordinate transformer that transforms a motion-dimension prediction value and a prediction error into those on a coordinate system the same as a first coordinate system, a filter that calculates a motion-dimension estimation value and an estimation error, a second coordinate transformer that transforms a motion-dimension estimation value and an estimation error into a component parallel to the route and a component vertical to the route and a motion-dimension prediction value and a prediction error, and a state determinator that determines a motion state of the target object. As a result, the frequency of an erroneous determination can be decreased.