A test piece characteristic estimation method includes estimating a moment of inertia of a test piece. A first transfer function G1 from a torque current command for a dynamometer to output from a shaft torque sensor is measured by vibrationally operating the dynamometer. A second transfer function G2 from the torque current command to the output of a dynamo rotation speed sensor is measured by vibrationally operating the dynamometer. A real part and an imaginary part of a ratio obtained by dividing the second transfer function G2 by the first transfer function G1 at a prescribed measurement frequency ωk are calculated. A moment of inertia Jeg and a rotational friction Ceg are estimated by using the real part and the imaginary part of the ratio.