A rotor position estimating device includes a voltage application unit, a current detecting unit and an estimating unit. The voltage application unit is configured to apply a d-axis voltage to an electric motor including a salient-pole rotor during a stop of the electric motor. The current detecting unit is configured to detect a q-axis current flowing through the electric motor at the time when the d-axis voltage is applied. The estimating unit is configured to estimate a rotor position during a stop of the electric motor on the basis of the q-axis current detected by the current detecting unit. The voltage application unit is configured to set a voltage application time in correspondence with peak timing at which the q-axis current reaches a peak in a transitional response characteristic of the q-axis current at the time when the d-axis voltage is applied.