A physical quantity estimating apparatus and method that detects an acceleration and deceleration rate of a vehicle body and a rotational velocity of a wheel, estimates at least one of a tire radius of each wheel, a road surface μ gradient, and a spring constant of a combination spring which combines spring elements, with a distribution ratio of braking force and driving force to a front and rear wheel and a distribution ratio of a load on each wheel that is corrected according to the detected acceleration and deceleration rate, as known values, based on a wheel speed difference of any two wheels, during acceleration and deceleration of a vehicle, of an ideal vehicle model that takes into consideration a tire torsional spring element and a suspension longitudinal spring element and estimates a tire type based on the estimated road surface μ gradient and spring constant.