A steering device, comprising: a speed reducer configured to decelerate a rotational power input from one surface side while increasing a torque of the rotational power and output rotation from an output section disposed on the other surface side; a motor provided on the one surface side and configured to input the rotational power to the speed reducer; and a control device configured to control the motor, wherein the speed reducer is connected to a steering unit provided on a vehicle, so as to cause the steering unit to steer a wheel by the torque, wherein the motor includes a rotor configured to generate the rotational power, wherein the rotor includes a rotor output shaft disposed coaxially with an output axis of the output section, wherein the motor inputs the rotational power from one end side of the rotor output shaft to the speed reducer, wherein the control device is disposed on the other end side of the rotor output shaft coaxially with the rotor output shaft and includes a sensing unit configured to sense rotation of the rotor, wherein the control device includes: an inverter circuit (C3I, C4I) configured to generate an electric current for controlling the motor; and a coupling unit (K1, K2) electrically connecting between the inverter circuit (C3I, C4I) and the motor, wherein the coupling unit (K1, K2) is disposed adjacent to the inverter circuit (C3I, C4I) and disposed to face the motor, and wherein the coupling unit (K1, K2) is further configured as a support structure detachably supporting a board (C3K, C4K) having the inverter circuit (C3I, C4I) provided thereon to a casing of the motor, characterized in that the output section has an arm provided thereon that is configured to rotate about the output axis in a circumferential direction of the output section, and the arm is configured to be disposed to project from the output section in a radial direction orthogonal to the output axis, and to connect to the steering unit. a speed reducer configured to decelerate a rotational power input from one surface side while increasing a torque of the rotational power and output rotation from an output section disposed on the other surface side; a motor provided on the one surface side and configured to input the rotational power to the speed reducer; and a control device configured to control the motor, wherein the speed reducer is connected to a steering unit provided on a vehicle, so as to cause the steering unit to steer a wheel by the torque, wherein the motor includes a rotor configured to generate the rotational power, wherein the rotor includes a rotor output shaft disposed coaxially with an output axis of the output section, wherein the motor inputs the rotational power from one end side of the rotor output shaft to the speed reducer, wherein the control device is disposed on the other end side of the rotor output shaft coaxially with the rotor output shaft and includes a sensing unit configured to sense rotation of the rotor, wherein the control device includes: an inverter circuit (C3I, C4I) configured to generate an electric current for controlling the motor; and a coupling unit (K1, K2) electrically connecting between the inverter circuit (C3I, C4I) and the motor, wherein the coupling unit (K1, K2) is disposed adjacent to the inverter circuit (C3I, C4I) and disposed to face the motor, and wherein the coupling unit (K1, K2) is further configured as a support structure detachably supporting a board (C3K, C4K) having the inverter circuit (C3I, C4I) provided thereon to a casing of the motor, characterized in that the output section has an arm provided thereon that is configured to rotate about the output axis in a circumferential direction of the output section, and the arm is configured to be disposed to project from the output section in a radial direction orthogonal to the output axis, and to connect to the steering unit. an inverter circuit (C3I, C4I) configured to generate an electric current for controlling the motor; and a coupling unit (K1, K2) electrically connecting between the inverter circuit (C3I, C4I) and the motor, wherein the coupling unit (K1, K2) is disposed adjacent to the inverter circuit (C3I, C4I) and disposed to face the motor, and wherein the coupling unit (K1, K2) is further configured as a support structure detachably supporting a board (C3K, C4K) having the inverter circuit (C3I, C4I) provided thereon to a casing of the motor, characterized in that the output section has an arm provided thereon that is configured to rotate about the output axis in a circumferential direction of the output section, and the arm is configured to be disposed to project from the output section in a radial direction orthogonal to the output axis, and to connect to the steering unit. the output section has an arm provided thereon that is configured to rotate about the output axis in a circumferential direction of the output section, and the arm is configured to be disposed to project from the output section in a radial direction orthogonal to the output axis, and to connect to the steering unit.