An electric power steering device comprising: a housing fixed to a fixed part so as not to rotate; a rotary shaft for steering rotatably provided to the housing and configured to rotate in accordance with an operation of a steering wheel and to apply a steering angle to steered wheels by the rotation; a worm wheel supported to a part of the rotary shaft for steering concentrically with the rotary shaft for steering within the housing and configured to rotate together with the rotary shaft for steering; a worm shaft comprises worm teeth provided on an axially intermediate part, the worm shaft of which parts except for the worm teeth being rotatably supported to the housing by bearings (9a, 9b) with the worm teeth being meshed with the worm wheel; and an electric motor provided to rotate the worm shaft; and a composite metal member, the composite metal member being capable of causing the worm shaft to oscillate and be displaced away from the worm wheel on the basis of deformation of the composite metal member when a temperature thereof becomes higher than a reference temperature, the composite metal member being capable of causing the worm shaft to oscillate and be displaced toward the worm wheel on the basis of deformation of the composite metal member when the temperature thereof becomes lower than the reference temperature, and characterized in that: the composite metal member is formed by laminating a plurality of metal plates having different thermal expansion coefficients, and the device further comprises a pressing member for pressing the worm shaft toward the worm wheel, wherein the composite metal member is provided between an end portion of the pressing member, which end portion is opposite to the worm shaft, and the inner peripheral surface of the housing, wherein the composite metal member can be deformed in a direction of suppressing a magnitude of a pressing force, by which the pressing member is to press the worm shaft toward the worm wheel, from increasing when a temperature thereof becomes higher than the reference temperature, and wherein the composite metal member can be deformed in a direction of suppressing the magnitude of the pressing force, by which the pressing member is to press the worm shaft toward the worm wheel, from decreasing when the temperature thereof becomes lower than the reference temperature. a housing fixed to a fixed part so as not to rotate; a rotary shaft for steering rotatably provided to the housing and configured to rotate in accordance with an operation of a steering wheel and to apply a steering angle to steered wheels by the rotation; a worm wheel supported to a part of the rotary shaft for steering concentrically with the rotary shaft for steering within the housing and configured to rotate together with the rotary shaft for steering; a worm shaft comprises worm teeth provided on an axially intermediate part, the worm shaft of which parts except for the worm teeth being rotatably supported to the housing by bearings (9a, 9b) with the worm teeth being meshed with the worm wheel; and an electric motor provided to rotate the worm shaft; and a composite metal member, the composite metal member being capable of causing the worm shaft to oscillate and be displaced away from the worm wheel on the basis of deformation of the composite metal member when a temperature thereof becomes higher than a reference temperature, the composite metal member being capable of causing the worm shaft to oscillate and be displaced toward the worm wheel on the basis of deformation of the composite metal member when the temperature thereof becomes lower than the reference temperature, and characterized in that: the composite metal member is formed by laminating a plurality of metal plates having different thermal expansion coefficients, and the device further comprises a pressing member for pressing the worm shaft toward the worm wheel, wherein the composite metal member is provided between an end portion of the pressing member, which end portion is opposite to the worm shaft, and the inner peripheral surface of the housing, wherein the composite metal member can be deformed in a direction of suppressing a magnitude of a pressing force, by which the pressing member is to press the worm shaft toward the worm wheel, from increasing when a temperature thereof becomes higher than the reference temperature, and wherein the composite metal member can be deformed in a direction of suppressing the magnitude of the pressing force, by which the pressing member is to press the worm shaft toward the worm wheel, from decreasing when the temperature thereof becomes lower than the reference temperature.