In hard disk drives, it is important to enlarge the control bandwidth in order to shorten the track pitch for larger data capacity. However, it is difficult for H_∞ control method to increase the control bandwidth if the mechanical resonance modes have uncertainty. This is because that the robustness of the H_∞ control method is assured by the small-gain theorem for additive or multiplicative perturbation and the control bandwidth is limitted by the uncertainty. In this study, we propose a H_∞ control method for high bandwidth design by introducing a new uncertainty model with a feedforward and a feedback path in order to reduce the conservatism of robust design. The effectiveness is shown by numerical simulations.