To provide a power steering device that satisfies both a requirement for a backlash amount and a requirement for a heat expansion.

The power steering device has: a worm wheel installed in a steering shaft; a worm shaft engaging with the worm wheel; an electric motor provided to one end side of the worm shaft to rotate the worm shaft; a biasing member provided to the other end side of the worm shaft to bias the worm shaft in an engaging direction with the worm wheel; a bearing provided to one end side of the worm shaft to support the worm shaft; a torque transmission member provided to the other end side of the worm shaft to transmit a rotational torque of the electric motor to the worm shaft, while holding the worm shaft so as to be swingable by a predetermined amount with respect to an output shaft of the electric motor; and an elastic member interposed between the output shaft of the electric motor and the worm shaft, and closer to the bearing from the torque transmission member to elastically support the worm shaft with respect to the output shaft of the electric motor.