A position sensor-less driving method is provided that can drive rotation speed/torque control of a permanent magnet motor using an inverter with an ideal sinusoidal current with the minimum number of switching, and can drive at a speed as low as an extremely low speed region close to zero speed. A neutral point potential of a permanent magnet motor is detected in synchronization with PWM waveform of the inverter. A rotor position of the permanent magnet motor is estimated from change of the neutral point potential. When the neutral point potential is detected, timing of each phase of the PWM waveform is shifted to generate three or four types of switch states of which output voltage of the inverter is not zero vector, and neutral point potentials in at least two types of switch states among them are sampled, whereby rotor position of the three-phase synchronous motor is estimated.