A deceleration factor estimating device that estimates a deceleration factor of a vehicle includes a road load calculating unit configured to calculate a road load estimated value, and a filtering calculating unit configured to perform filtering processing of extracting a predetermined frequency component of the road load estimated value calculated by the road load calculating unit. The filtering calculating unit extracts a vehicle-originated road load component, an environment-originated road load component, and the like by filtering the road load estimated value to extract a certain predetermined frequency component.