PURPOSE: To obtain a motor drive circuit for producing high torque and having short starting time by switching the number of armature coils to be conducted for the interval after start before constant speed rotation, the interval after brake operation before stoppage, and the constant speed rotation interval.

CONSTITUTION: Upon turn ON of a motor, the rotor is accelerated. At that time, a rotational speed lock signal is High and switching elements 2U, 2V, 2W are closed. Consequently, only three coils Cu1, Cv2, Cw1 are conducted. When the motor enters into constant speed rotation, the rotational speed lock signal goes Low and the switching elements 2U, 2V, 2W are opened. At that time, coils Cu1, Cu2 in phase U, coils Cv1, Cv2 in phase V and coils Cw1, Cw2 in phase W are conducted thus conducting all driving coils. The rotation lock signal is High during the interval after turn OFF of the motor before stoppage of rotor thus conducting only the driving coils Cu1, Cv2, Cw1.