A rotor position sensorless multiphase motor driving device includes a rotor; a plurality of phase windings; a common terminal to which one terminal of terminals at both ends of each winding is star connected; an upper-side drive transistor and a lower-side drive transistor connected to the other terminal of the winding; a commutation control unit operable to select two terminals other than the common terminal of the windings, and to turn on the corresponding pair of upper-side drive transistor and the lower-side drive transistor; a rotor position search pulse applying unit operable to apply a search pulse to the selected two terminals; and a comparing unit operable to detect a rotor position based on a response signal generated between the terminal which was unselected and the common terminal according to the search pulse application.