Motor drive device

A motor drive device comprising:

• a motor having a rotor and a drive coil;
• a rotor position detector that detects position information of the rotor;
• a speed detector that converts the position information into speed information;
• a direction detector that converts the position information into rotating direction information;
• and
• a drive unit that drives the motor,
• wherein, in a state in which a drive command is inputted to the drive unit and the motor is driven, the motor drive device determines that the motor is locked and turns off a drive output of the drive unit upon detection of any one of a case where a pulse of a rotor position detector signal is not inputted from the rotor position detector into the speed detector and another case where a change of rotating direction of the motor is detected by the direction detector during measurement of a time interval between rising edges or between falling edges of the pulse of the rotor position detector signal from the rotor position detector in a state in which the rotor repeats a forward rotation and a backward rotation in a condition that the rotor is locked.