An electric power steering apparatus includes; a DC brush motor, and a boss arranged between an output shaft of the motor and an input shaft driven by the motor, for transmitting a rotational force of the motor from the output shaft to the input shaft by the boss per se. A weight of the boss is equal to or larger than 10% of a weight of a rotor of the motor. An electric power steering apparatus includes; a DC brush motor and a boss arranged between the output shaft of the motor and the input shaft driven by the motor, for transmitting the rotational force of the motor from the output shaft to the input shaft by the boss per se. A moment of inertia of the boss is equal to or larger than 10% of a moment of inertia of the rotor of the motor.