An integral-type electric power steering device comprising: a motor component including a motor that generates an assist torque corresponding to a steering torque caused by a driver in a car and applies the generated assist torque to a steering shaft of the car via a reduction mechanism ; and a control device including control-circuit elements for controlling the motor in a state where the motor component , the reduction mechanism , and the control device are integrally fixed; wherein the control device includes at least heating elements such as a microcomputer and an FET-driving circuit, which generate heat when operated, a control board on which the heating elements are mounted, a power board on which a power semiconductor element is mounted, a mechanism component , to which the control board and the power board are fixed and an inner space of the control device which includes the control board and the power board ; and heat generated by the power semiconductor element is conducted to the mechanism component , while at least a part of the heat, which is generated by the heating elements , is conducted to the mechanism component via a thermal-conductive component , wherein the control device is arranged between the reduction mechanism and the motor component , and the mechanism component includes a reduction-mechanism-side case , which is connected to the reduction mechanism , and a motor-side case , which is connected to the motor component , and the control board is fixed to the reduction mechanism-side case , and the heating elements are mounted on a surface of the control board , which faces to a wall surface of the reduction-mechanism-side case , and the thermal-conductive component is arranged between the heating elements and the wall surface of the reduction-mechanism-side case ; characterized in that the reduction-mechanism-side case includes a convex portion , which is contacted to the thermal-conductive component , on the wall surface. a motor component including a motor that generates an assist torque corresponding to a steering torque caused by a driver in a car and applies the generated assist torque to a steering shaft of the car via a reduction mechanism ; and a control device including control-circuit elements for controlling the motor in a state where the motor component , the reduction mechanism , and the control device are integrally fixed; wherein the control device includes at least heating elements such as a microcomputer and an FET-driving circuit, which generate heat when operated, a control board on which the heating elements are mounted, a power board on which a power semiconductor element is mounted, a mechanism component , to which the control board and the power board are fixed and an inner space of the control device which includes the control board and the power board ; and heat generated by the power semiconductor element is conducted to the mechanism component , while at least a part of the heat, which is generated by the heating elements , is conducted to the mechanism component via a thermal-conductive component , wherein the control device is arranged between the reduction mechanism and the motor component , and the mechanism component includes a reduction-mechanism-side case , which is connected to the reduction mechanism , and a motor-side case , which is connected to the motor component , and the control board is fixed to the reduction mechanism-side case , and the heating elements are mounted on a surface of the control board , which faces to a wall surface of the reduction-mechanism-side case , and the thermal-conductive component is arranged between the heating elements and the wall surface of the reduction-mechanism-side case ; characterized in that the reduction-mechanism-side case includes a convex portion , which is contacted to the thermal-conductive component , on the wall surface. <EOS>