An electric power steering apparatus, comprising: - a torque sensor which detects a steering torque, Tn, applied to a steering shaft by a driver; - a motor which applies an assist torque for assisting steering to the steering shaft; - a vehicle speed sensor which detects a vehicle speed, Vx; - an assist command calculation unit which calculates an assist command in response to the steering torque detected by the torque sensor and the vehicle speed detected by the vehicle speed sensor; - a motor controlling device which controls the assist torque of the motor in response to the assist command calculated by the assist command calculation unit; - an abnormality detection unit which detects an abnormality generated in an electric power steering apparatus body; - an assist command switching unit adapted to switch the assist command to an assist command at an abnormal time, and characterised by further comprising: - a steering burden estimation unit which estimates a steering burden of the driver on the basis of at least any one signal of a rotational angular velocity, θ', of the motor detected from the motor, the steering torque, Tn, and the vehicle speed, Vx, wherein: - if the abnormality detection unit detects an abnormality, the assist command switching unit switches the assist command to the assist command at an abnormal time, thereby continuing control of the assist torque of the motor in response to the assist command at an abnormal time; - if, whilst an abnormality is detected, the steering burden estimated by the steering burden estimation unit is small; then it is determined that there is an abnormality in a first range and the assist command at an abnormal time in this first range is set smaller than that at a normal time; - if, whilst an abnormality is detected, the steering burden estimated by the steering burden estimation unit is larger than in the first range, then it is determined that there is an abnormality in a second range and the assist command at an abnormal time in this second range is increased, as compared with the first range, to a size near or equal to that at a normal time; and thus the assist torque is increased or decreased in response to the steering burden. - a torque sensor which detects a steering torque, Tn, applied to a steering shaft by a driver; - a motor which applies an assist torque for assisting steering to the steering shaft; - a vehicle speed sensor which detects a vehicle speed, Vx; - an assist command calculation unit which calculates an assist command in response to the steering torque detected by the torque sensor and the vehicle speed detected by the vehicle speed sensor; - a motor controlling device which controls the assist torque of the motor in response to the assist command calculated by the assist command calculation unit; - an abnormality detection unit which detects an abnormality generated in an electric power steering apparatus body; - an assist command switching unit adapted to switch the assist command to an assist command at an abnormal time, and - a steering burden estimation unit which estimates a steering burden of the driver on the basis of at least any one signal of a rotational angular velocity, θ', of the motor detected from the motor, the steering torque, Tn, and the vehicle speed, Vx, wherein: - if the abnormality detection unit detects an abnormality, the assist command switching unit switches the assist command to the assist command at an abnormal time, thereby continuing control of the assist torque of the motor in response to the assist command at an abnormal time; - if, whilst an abnormality is detected, the steering burden estimated by the steering burden estimation unit is small; then it is determined that there is an abnormality in a first range and the assist command at an abnormal time in this first range is set smaller than that at a normal time; - if, whilst an abnormality is detected, the steering burden estimated by the steering burden estimation unit is larger than in the first range, then it is determined that there is an abnormality in a second range and the assist command at an abnormal time in this second range is increased, as compared with the first range, to a size near or equal to that at a normal time; and thus the assist torque is increased or decreased in response to the steering burden.