We previously proposed a multivariable identification method, called the "decoupling identification method", for a horizontal two-link robot arm with elastic harmonic drive gears. This paper extends the identification method to a vertical two-link robot arm with the harmonic drive gears and timing belts, under gravity. The mechanical resonance effects of the timing belts in the high-frequency range are decimated in advance, to apply the decoupling method. The characteristics of the timing belts are independently estimated as perturbations in the high-frequency range for robust controller design. The effectiveness of the extended identification method was experimentally verified using the vertical two-link robot with the elastic elements.