To provide an electric power steering device capable of preventing the occurrence of insufficient output and preventing the other electrical equipments from being adversely affected owing to the cooperation with a car navigation device.

This electric power steering device includes a main power supply 9 for supplying electric power to a motor 4, auxiliary power supply 10 for supplying electric power to the motor 4, a charging and discharging circuit 13 for forming a first output condition for charging the auxiliary power supply 10 based on the main power supply 9 and supplying electric power to the motor 4 by only the main power supply 9 and a second output condition for supplying electric power to the motor 4 from the main power supply 9 and the auxiliary power supply 10 selectively, and a control circuit 6 for receiving the information about navigation from the car navigation device 30 capable of transmitting the information about navigation to the outside, determining whether a vehicle exists in a high speed steering predicting area or not based on the information about navigation, putting the charging and discharging circuit 13 into the second output condition if it is determined that the vehicle exists in the high speed steering predicting area, and putting the charging and discharging circuit 13 into the first output condition if it is determined that the vehicle does not exist in the area.