An apparatus for diagnosing an abnormality in a torque sensor that is connected to a controller of an electric power steering apparatus by two systems includes a steering speed determination unit that determines whether a variation speed of a steering angle equals or exceeds a predetermined speed on the basis of a detection result from a steering angle sensor, an integrated value calculation unit that calculates an integrated value of an input torque detected by the torque sensor within a sampling period extending from a point at which a steering wheel is steered at or above the predetermined speed to a point at which the steering wheel returns to a neutral position, and an abnormality determination unit that determines that an abnormality has occurred in the torque sensor when the integrated value of the input torque is equal to or smaller than a predetermined reference integrated torque.