A control device of an AC rotating machine, comprising: - current vector detection means for detecting a current vector of the AC rotating machine; - magnetic-pole position computation means for computing an estimated magnetic-pole position of the AC rotating machine, - control means for receiving a current vector instruction and the detection current vector as inputs and outputting a voltage vector instruction obtained by adding a fundamental voltage vector instruction to drive the AC rotating machine and an alternating voltage vector instruction alternating to a direction indicated by the estimated magnetic-pole position; - voltage application means for applying a voltage to the AC rotating machine according to the voltage vector instruction; the control device being characterized by further comprising: - alternating current amplitude computation means for receiving a current vector detected by the current vector detection means as an input and computing an alternating current amplitude of at least one of a parallel component and an orthogonal component with respect to the alternating voltage vector instruction; - alternating current amplitude instruction generation means for generating an alternating current amplitude instruction by multiplying the current vector instruction or the detection current vector by a predetermined amplification value, which is determined from the current vector instruction and the alternating current amplitude, or by a predetermined amplification value, which is determined from detection current vector and the alternating current amplitude; and wherein the magnetic-pole position computation means is adapted to compute the estimated magnetic-pole position so that the alternating current amplitude coincides with the alternating current amplitude instruction based on a deviation between the alternating current amplitude instruction and the alternating current amplitude. - current vector detection means for detecting a current vector of the AC rotating machine; - magnetic-pole position computation means for computing an estimated magnetic-pole position of the AC rotating machine, - control means for receiving a current vector instruction and the detection current vector as inputs and outputting a voltage vector instruction obtained by adding a fundamental voltage vector instruction to drive the AC rotating machine and an alternating voltage vector instruction alternating to a direction indicated by the estimated magnetic-pole position; - voltage application means for applying a voltage to the AC rotating machine according to the voltage vector instruction; - alternating current amplitude computation means for receiving a current vector detected by the current vector detection means as an input and computing an alternating current amplitude of at least one of a parallel component and an orthogonal component with respect to the alternating voltage vector instruction; - alternating current amplitude instruction generation means for generating an alternating current amplitude instruction by multiplying the current vector instruction or the detection current vector by a predetermined amplification value, which is determined from the current vector instruction and the alternating current amplitude, or by a predetermined amplification value, which is determined from detection current vector and the alternating current amplitude; and