To measure easily at least one of spring modulus, phase lag, and damping coefficient of tires in vibration condition.

While making a tire supporter with a tire supporting section to support a tire, a vibration exciter consisting of a push plate and a vibrating means capable of reciprocating to vibrate the push plate in the tire-radial direction, the tire-shaft direction or the tire-perimeter direction is connected to ground at the push plate. Also, while vibrating the tire by the vibrating means, at least one of the spring modulus. the phase lag and the damping coefficient of tires in vibration condition is computed from the data of displacement of the push plate as well as the data of axial force in the tire-radial direction, the tire-shaft direction or the tire-perimeter direction acting to the tire supporting section.