A rotor phase/speed estimating device includes a high-frequency voltage injection unit, a high-frequency current amplitude detection unit of a fundamental wave component, a correlation signal generation unit, and a rotor phase generation unit. The high-frequency voltage injection unit applies a high-frequency voltage to an AC motor. The high-frequency current amplitude detection unit of a fundamental wave component detects a primary Fourier coefficient equivalent value. The correlation signal generation unit is arranged to generate a correlation signal using the Fourier coefficient equivalent value. The rotor phase generation unit is arranged to generate an estimated value of the rotor phase and an estimated value of a rotor speed using the correlation signal.