To provide an electric power steering device capable of securing durability, without enlarging an outer diameter of a circulating part of a ball screw.

This electric power steering device includes an electric motor, a rack shaft 7 connected between a steering mechanism and a tie rod, and a power transmission mechanism for transmitting power from the electric motor to the rack shaft 7. The power transmission mechanism is constituted of: a screw shaft 9 connected to or integrated with the rack shaft 7 and having a male screw groove; and a ball screw mechanism having a nut arranged around the screw shaft and having a female screw groove, and a plurality of rolling elements rollable between the male screw groove and the female screw groove. In at least one in a stroke end of the rack shaft 7, a load bearing power reducing area LA of the nut is set to be positioned in an area except for a phase position φp and φp' in the rack shaft circumferential direction defined by a plane formed of the rack shaft 7 and the tie rod connected to the rack shaft.