This paper describes that the proposed method is able to evaluate accurately the resistant torque acting on rotating spindle system which includes rolling bearing, under high-dm N condition lower than two million mm rpm. The resistant torque is calculated as the product of the angular acceleration during free-running and the equivalent moment of inertia of spindle. The acceleration is calculated from the accurate measurement of change in series of each rotation-cycle under free-running. The equivalent moment of inertia is the sum of the moment of inertia of spindle rotor, the effect of rolling elements and the effect of retainer for the elements.