An electric power steering device for a vehicle includes an estimation mechanism estimating if there is a possibility that a backward electric current flows in a booster circuit toward a vehicle battery device, and a boosting controller stopping the boosting operation of the booster circuit to prevent a backward electric current from flowing in the booster circuit when it is estimated that there is a possibility that a backward electric current flows by the estimation mechanism. The estimation mechanism estimates that there is a possibility that a backward electric current flows in the booster circuit when the steering condition of a steering wheel is a returning condition or a steering-held condition. Otherwise, the estimation mechanism estimates if a backward electric current flows on the basis of input and output voltages of the booster circuit and information on the switching of a first boosting switching element. Thereby, overheat of the booster circuit can be prevented.