[Problem] An object of the present invention is to provide an electric power steering apparatus that realizes protecting of Zener diodes without impairing steering performances by time-integrating a loss power of the Zener diodes for protecting FETs and gradually limiting a duty ratio with an increase in an integrating loss even though a power-source voltage drops. [Means for solving the problem] An electric power steering apparatus that calculates a steering assist command value based on a steering torque and a vehicle velocity, generates a PWM-signal, and performs an assist control of a steering system by PWM-driving a motor through an FET bridge circuit having Zener diodes, comprising: a loss power calculating section that calculates a loss power when a difference between an ignition voltage and an inverter applying voltage is equal to or more than a predetermined voltage; an integrating loss calculating section to calculate an integrating loss of the loss power; a permissible loss calculating section to calculate a permissible loss based on a temperature; a minimum value selecting section to select a minimum value of a loss difference of the permissible loss and the integrating loss; and a limit value calculating section to calculate a limit value of the PWM-signal based on the minimum value of the loss difference and the permissible loss.