A permanent-magnet synchronous motor comprising: an inverter power circuit including a plurality of switching elements (31 to 36) that are switched to convert direct-current power to three-phase alternating-current power; a motor body to be driven by the three-phase alternating-current power, the motor body including a stator and a rotor; a current detector to calculate an excitation current value (Id) and a torque current value (Iq) from respective motor current values (Iu, Iv) of two phases of the stator and an estimated value (θ ~ ) of a magnetic pole position of the rotor, the motor current values (Iu, Iv) being detected by a first shunt resistor and a second shunt resistor , respectively, each of the resistors being serially connected to the switching elements of the inverter power circuit ; a voltage detector to detect a direct-current bus voltage (Vdc) being input to the inverter power circuit , a magnetic pole position detector to determine, for output to the current detector , the estimated value (θ ~ ) from the excitation current value (Id), the torque current value (Iq), and supply voltage information (Vd*, Vq*); a velocity calculation unit for calculating an angular velocity (ωr) from the estimated value (θ ~ ); a voltage calculation unit to calculate, by means of the excitation current value (Id), the torque current value (Iq), the direct-current bus voltage (Vdc) and the angular velocity (ωr), the supply voltage information (Vd*, Vq*) that causes the torque current value (Iq) to approximate a torque current command value (Iq*); an inverter controller to control the inverter power circuit on the basis of the supply voltage information (Vd*, Vq*) and the estimated value (θ ~ ); characterised by a torque current command generation unit to calculate the torque current command value (Iq*) from an operational air volume command and the angular velocity (ωr). an inverter power circuit including a plurality of switching elements (31 to 36) that are switched to convert direct-current power to three-phase alternating-current power; a motor body to be driven by the three-phase alternating-current power, the motor body including a stator and a rotor; a current detector to calculate an excitation current value (Id) and a torque current value (Iq) from respective motor current values (Iu, Iv) of two phases of the stator and an estimated value (θ ~ ) of a magnetic pole position of the rotor, the motor current values (Iu, Iv) being detected by a first shunt resistor and a second shunt resistor , respectively, each of the resistors being serially connected to the switching elements of the inverter power circuit ; a voltage detector to detect a direct-current bus voltage (Vdc) being input to the inverter power circuit , a magnetic pole position detector to determine, for output to the current detector , the estimated value (θ ~ ) from the excitation current value (Id), the torque current value (Iq), and supply voltage information (Vd*, Vq*); a velocity calculation unit for calculating an angular velocity (ωr) from the estimated value (θ ~ ); a voltage calculation unit to calculate, by means of the excitation current value (Id), the torque current value (Iq), the direct-current bus voltage (Vdc) and the angular velocity (ωr), the supply voltage information (Vd*, Vq*) that causes the torque current value (Iq) to approximate a torque current command value (Iq*); an inverter controller to control the inverter power circuit on the basis of the supply voltage information (Vd*, Vq*) and the estimated value (θ ~ ); characterised by a torque current command generation unit to calculate the torque current command value (Iq*) from an operational air volume command and the angular velocity (ωr). <EOS>