A motor device comprising: a motor comprising a motor shaft protruded from a motor main body; a worm gear which is connected with the motor shaft through a transmission mechanism and is formed with a spiral groove on an outer peripheral face; and a worm wheel which is engaged with the worm gear; wherein the transmission mechanism comprises a transmission member for transmitting rotation of the motor shaft to the worm gear at a position facing an end face on a motor main body side of the worm gear in an axial line direction of the worm gear; wherein one of the end face on the motor main body side of the worm gear and an end face on a worm gear side of the transmission member is formed with two protruded parts which are protruded toward the other of the end faces at positions separated in a radial direction, and a recessed part engaged with the two protruded parts is formed in the other of the end faces; characterized in that: the worm gear is made of resin and is formed with a spring arrangement hole which is coaxially extended in the axial line direction of the worm gear in an inside of the worm gear from the end face on the motor main body side of the worm gear; a compression coil spring, which urges the transmission member towards the motor shaft side is disposed in the inside of the spring arrangement hole and between the two protruded parts in the radial direction; the inside of the worm gear is formed with a communicating hole which is in communication with the spring arrangement hole and is extended in the axial line direction on an opposite side to the motor main body side with respect to the spring arrangement hole; an inner diameter of the communicating hole is smaller than an inner diameter of the spring arrangement hole, so that a ring-shaped step part, which is formed in a connected portion of the spring arrangement hole with the communicating hole, is formed to be a spring receiving face, which receives an end part of the compression coil spring on an opposite side to the motor main body side; and a sum of a dimension in the axial line direction of the spring arrangement hole and a dimension in the axial line direction of the communicating hole is longer than a dimension of a region where the spiral groove is formed on the outer peripheral face of the worm gear. a motor comprising a motor shaft protruded from a motor main body; a worm gear which is connected with the motor shaft through a transmission mechanism and is formed with a spiral groove on an outer peripheral face; and a worm wheel which is engaged with the worm gear; wherein the transmission mechanism comprises a transmission member for transmitting rotation of the motor shaft to the worm gear at a position facing an end face on a motor main body side of the worm gear in an axial line direction of the worm gear; the worm gear is made of resin and is formed with a spring arrangement hole which is coaxially extended in the axial line direction of the worm gear in an inside of the worm gear from the end face on the motor main body side of the worm gear; a compression coil spring, which urges the transmission member towards the motor shaft side is disposed in the inside of the spring arrangement hole and between the two protruded parts in the radial direction; the inside of the worm gear is formed with a communicating hole which is in communication with the spring arrangement hole and is extended in the axial line direction on an opposite side to the motor main body side with respect to the spring arrangement hole; an inner diameter of the communicating hole is smaller than an inner diameter of the spring arrangement hole, so that a ring-shaped step part, which is formed in a connected portion of the spring arrangement hole with the communicating hole, is formed to be a spring receiving face, which receives an end part of the compression coil spring on an opposite side to the motor main body side; and a sum of a dimension in the axial line direction of the spring arrangement hole and a dimension in the axial line direction of the communicating hole is longer than a dimension of a region where the spiral groove is formed on the outer peripheral face of the worm gear.