A sensorless control apparatus of a synchronous motor, comprising: a PWM processing unit configured to pulse-width modulate each three-phase voltage command, based on comparison between the three-phase voltage command and a PWM carrier, and thereby generates a gate command for an inverter; a high-frequency voltage calculator configured to obtain high-frequency voltage components by calculating an applying voltage value applied to the synchronous motor from the inverter configured to use an output signal of the PWM processing unit, and configured to calculate sine components and cosine components of a plurality of frequencies not lower than a carrier frequency of the PWM carrier included in the applying voltage; a high-frequency current calculator configured to obtain high-frequency current components by calculating said sine components and cosine components of the plurality of frequencies not lower than the carrier frequency, wherein said high-frequency voltage components are included in a current response value from the synchronous motor driven by the inverter; and an estimated angle calculator configured to calculate an estimated phase angle indicative of an estimated value of an angle of rotation of the synchronous motor, based on two pairs selected from a plurality of pairs each including the high-frequency voltage component and the high-frequency current component each of which includes a cosine component and a sine component at an equal frequency, the pairs obtained for at least two different frequencies; characterized in that one of the selected high-frequency voltage components has a greatest absolute value and another one of the selected high-frequency voltage components has greatest components in a direction perpendicular to the one of the selected high-frequency voltage components. a PWM processing unit configured to pulse-width modulate each three-phase voltage command, based on comparison between the three-phase voltage command and a PWM carrier, and thereby generates a gate command for an inverter; a high-frequency voltage calculator configured to obtain high-frequency voltage components by calculating an applying voltage value applied to the synchronous motor from the inverter configured to use an output signal of the PWM processing unit, and configured to calculate sine components and cosine components of a plurality of frequencies not lower than a carrier frequency of the PWM carrier included in the applying voltage; a high-frequency current calculator configured to obtain high-frequency current components by calculating said sine components and cosine components of the plurality of frequencies not lower than the carrier frequency, wherein said high-frequency voltage components are included in a current response value from the synchronous motor driven by the inverter; and an estimated angle calculator configured to calculate an estimated phase angle indicative of an estimated value of an angle of rotation of the synchronous motor, based on two pairs selected from a plurality of pairs each including the high-frequency voltage component and the high-frequency current component each of which includes a cosine component and a sine component at an equal frequency, the pairs obtained for at least two different frequencies; characterized in that one of the selected high-frequency voltage components has a greatest absolute value and another one of the selected high-frequency voltage components has greatest components in a direction perpendicular to the one of the selected high-frequency voltage components.