An electric power steering device for a vehicle comprises estimation means for estimating if there is a possibility that a backward electric current flows in a booster circuit 40 toward a vehicle battery device 100, and boosting control means for stopping the boosting operation of the booster circuit 40 to prevent a backward electric current from flowing in the booster circuit 40 when it is estimated that there is a possibility that a backward electric current flows by the estimation means. The estimation means estimates that there is a possibility that a backward electric current flows in the booster circuit 40 when the steering condition of a steering wheel 11 is a returning condition or a steering-held condition. Otherwise, the estimation means estimates if a backward electric current flows on the basis of input and output voltages of the booster circuit 40 and information on the switching of a first boosting switching element 43. Thereby, overheat of the booster circuit 40 can be prevented.
