An electric power steering apparatus including an electric motor that outputs an assist torque for a steering wheel of a vehicle, a speed reducer that decelerates rotations of the electric motor, and a control device that controls driving of the electric motor, wherein: the control device is disposed coaxially with an output shaft of the electric motor between the electric motor and the speed reducer; and the control device includes: a heat sink that is made of a metal material having high heat conductivity, a power circuit board that has a bridge circuit formed of a plurality of semiconductor switching elements (Q1-Q6) to switch a current of the electric motor according to a torque assisting the steering wheel and is fixed to the heat sink, a control circuit board that has a control circuit generating a drive signal to control the bridge circuit on the basis of a steering torque of the steering wheel and is electrically connected to the power circuit board via an electric conductor, an electronic relay circuit board that has an electronic relay circuit passing and interrupting a motor current to be supplied to the electric motor and is electrically connected to the power circuit board via the electric conductor, and a housing to which the electronic relay circuit board is attached and in which the power circuit board and the control circuit board are housed for protection, characterized in that the power circuit board, the control circuit board, the electronic relay circuit board, and the housing are disposed concentrically with the output shaft of the electric motor. the control device is disposed coaxially with an output shaft of the electric motor between the electric motor and the speed reducer; and the control device includes: a heat sink that is made of a metal material having high heat conductivity, a power circuit board that has a bridge circuit formed of a plurality of semiconductor switching elements (Q1-Q6) to switch a current of the electric motor according to a torque assisting the steering wheel and is fixed to the heat sink, a control circuit board that has a control circuit generating a drive signal to control the bridge circuit on the basis of a steering torque of the steering wheel and is electrically connected to the power circuit board via an electric conductor, an electronic relay circuit board that has an electronic relay circuit passing and interrupting a motor current to be supplied to the electric motor and is electrically connected to the power circuit board via the electric conductor, and a housing to which the electronic relay circuit board is attached and in which the power circuit board and the control circuit board are housed for protection, characterized in that the power circuit board, the control circuit board, the electronic relay circuit board, and the housing are disposed concentrically with the output shaft of the electric motor. a heat sink that is made of a metal material having high heat conductivity, a power circuit board that has a bridge circuit formed of a plurality of semiconductor switching elements (Q1-Q6) to switch a current of the electric motor according to a torque assisting the steering wheel and is fixed to the heat sink, a control circuit board that has a control circuit generating a drive signal to control the bridge circuit on the basis of a steering torque of the steering wheel and is electrically connected to the power circuit board via an electric conductor, an electronic relay circuit board that has an electronic relay circuit passing and interrupting a motor current to be supplied to the electric motor and is electrically connected to the power circuit board via the electric conductor, and a housing to which the electronic relay circuit board is attached and in which the power circuit board and the control circuit board are housed for protection, characterized in that the power circuit board, the control circuit board, the electronic relay circuit board, and the housing are disposed concentrically with the output shaft of the electric motor.