An electric power steering device for a vehicle, comprising: at least one electric motor for adding a predetermined assist force for assisting a steering wheel manipulation by a driver; a plurality of assist systems (U1, V1, W1, 25; U2, V2, W2, 26) including said electric motor, said assist systems (U1, V1, W1, 25; U2, V2, W2, 26) electromagnetically driving said electric motor; assist control means for calculating an assist amount representing said predetermined assist force by using a manipulation force input by said driver via a steering wheel and controlling an assist to said steering wheel manipulation by using at least one of said assist systems (U1, V1, W1, 25; U2, V2, W2, 26) on the basis of said calculated assist amount, characterized in that when a malfunction occurs in at least one of said assist systems (U1, V1, W1, 25; U2, V2, W2, 26), said assist control means is configured to: calculate an assist amount at one of vehicle stopping and moving while controlling a maximum assist amount at the vehicle stopping representing a maximum assist force added by said electric motor at the vehicle stopping when a malfunction occurs to an amount smaller than a maximum assist amount at the vehicle moving representing a maximum assist force added by said electric motor at the vehicle moving when a malfunction occurs and being a malfunction state upper limit; control the assist to said steering wheel manipulation by using said assist system (U1, V1, W1, 25; U2, V2, W2, 26) under a normal state other than said assist system (U1, V1, W1, 25; U2, V2, W2, 26) under a malfunction state on the basis of said calculated assist amount at the vehicle stopping or moving; and when the vehicle is stopped, control the assist to said steering wheel manipulation by using said assist system (U1, V1, W1, 25; U2, V2, W2, 26) under a normal state on the basis of said calculated assist amount at the vehicle stopping. at least one electric motor for adding a predetermined assist force for assisting a steering wheel manipulation by a driver; a plurality of assist systems (U1, V1, W1, 25; U2, V2, W2, 26) including said electric motor, said assist systems (U1, V1, W1, 25; U2, V2, W2, 26) electromagnetically driving said electric motor; assist control means for calculating an assist amount representing said predetermined assist force by using a manipulation force input by said driver via a steering wheel and controlling an assist to said steering wheel manipulation by using at least one of said assist systems (U1, V1, W1, 25; U2, V2, W2, 26) on the basis of said calculated assist amount, characterized in that when a malfunction occurs in at least one of said assist systems (U1, V1, W1, 25; U2, V2, W2, 26), said assist control means is configured to: calculate an assist amount at one of vehicle stopping and moving while controlling a maximum assist amount at the vehicle stopping representing a maximum assist force added by said electric motor at the vehicle stopping when a malfunction occurs to an amount smaller than a maximum assist amount at the vehicle moving representing a maximum assist force added by said electric motor at the vehicle moving when a malfunction occurs and being a malfunction state upper limit; control the assist to said steering wheel manipulation by using said assist system (U1, V1, W1, 25; U2, V2, W2, 26) under a normal state other than said assist system (U1, V1, W1, 25; U2, V2, W2, 26) under a malfunction state on the basis of said calculated assist amount at the vehicle stopping or moving; and when the vehicle is stopped, control the assist to said steering wheel manipulation by using said assist system (U1, V1, W1, 25; U2, V2, W2, 26) under a normal state on the basis of said calculated assist amount at the vehicle stopping. calculate an assist amount at one of vehicle stopping and moving while controlling a maximum assist amount at the vehicle stopping representing a maximum assist force added by said electric motor at the vehicle stopping when a malfunction occurs to an amount smaller than a maximum assist amount at the vehicle moving representing a maximum assist force added by said electric motor at the vehicle moving when a malfunction occurs and being a malfunction state upper limit; control the assist to said steering wheel manipulation by using said assist system (U1, V1, W1, 25; U2, V2, W2, 26) under a normal state other than said assist system (U1, V1, W1, 25; U2, V2, W2, 26) under a malfunction state on the basis of said calculated assist amount at the vehicle stopping or moving; and when the vehicle is stopped, control the assist to said steering wheel manipulation by using said assist system (U1, V1, W1, 25; U2, V2, W2, 26) under a normal state on the basis of said calculated assist amount at the vehicle stopping.