Abstract: In order to achieve low cost, small size, and light weight, to improve response at the time of transmission of power, and to prevent the occurrence of unusual noise, a power transmission device (10) of an electric power steering device (1) has a motor section (5) comprising a rotational shaft (7), a rotor (51) attached to an inner end side (7a) of the rotational shaft (7), and a stator (52) positioned opposite to the rotor (51), a worm gear (61) attached to a distal end side (7b) from the motor section (5) on the rotational shaft (7), and a worm wheel gear (62) engaged with the gear (61). The rotational shaft (7) is rotatably supported by first and second bearings (81, 82), the first bearing (81) being held by a housing (4) at a distal end side (7b) to the worm gear (61). The second bearing (82) is held by the housing (4) between the worm gear (61) and the rotor (51) so that the worm gear (61) is sandwiched between the first and second bearings (81, 82).