1. A control device for rotary machine, which controls a rotary machine having windings for n phases (n is a natural number equal to or greater than 3), the control device comprising: a voltage application section for applying a voltage vector based on a voltage vector instruction, to the rotary machine; a current detection section for detecting current flowing in the winding for each phase of the rotary machine; a voltage vector instruction calculation section for calculating, as the voltage vector instruction, 2n voltage vector instructions having the same amplitude, phases separated at equal intervals in one period (360 degrees), and the same application time, and outputting the 2n voltage vector instructions to the voltage application section; a storage section for storing, as stored current values, 2n×n currents detected for the respective phases by the current detection section when the 2n voltage vectors are applied, under the same condition thereamong; a position estimation section for estimating a rotor position of the rotary machine in a stopped state, based on the stored current values from the storage section; and an adjustment section for adjusting the application time to a minimum necessary application time Ta that allows the rotary machine to become a magnetically saturated state when the voltage vectors are applied, so as to enable the estimation of the rotor position, wherein the adjustment section calculates an adjustment evaluation value based on the ratio between a voltage amplitude value of the voltage vector instructions and the stored current values from the current detection section in the case where the voltage vector based on the voltage vector instruction is applied with the application time being set to an arbitrary application time Tm, and adjusts the application time based on the adjustment evaluation value.