To reduce noise generated when a worm is radially moved by an engaging reaction force by a simple constitution, and besides, to facilitate the incorporation of the worm and a pressing element for supporting the worm.

An electric power steering device comprises a pressing element 7 to support a shaft 1b of the worm 1 and movable in a direction in which the worm 1 is pressed against a worm wheel 2; a coil spring 9 to energize the pressing element 7; and a guide hole 35 containing the pressing element 7 and guiding the movement of the pressing element 7, an air reservoir 37 to suppress the movement of the pressing element 7 by the coil spring 9 to the side opposite to the coil spring 9 is provided in the pressing element 7 in the guide hole 35, and further, a throttle hole 38 opened to the air reservoir 37 is formed.