An electric power supply device capable of miniaturizing an FET and wiring and reducing the amount of heat generation even when a motor load goes into a lock state is provided. It is determined whether or not a lock current flows in a motor M1 by comparing various determination voltages with a voltage Vds between a drain and a source of a MOSFET (T1), and in the case of detecting that the lock current flows, an operation of turning off the MOSFET (T1) until a retry cycle to elapses after turning on the MOSFET (T1) for only energization time tb for which lock torque can be caused is repeatedly executed. Then, when a motor current ID becomes smaller than the lock current, control of returning the MOSFET (T1) to a normal operation is performed. Consequently, the lock current can be prevented from flowing continuously.