A motor control unit that controls a three-phase motor with multi-system motor windings via motor driving circuits (120A, 120B) for respective winding systems based on a current command value, wherein said motor control unit comprises: current detecting circuits (121A, 121B) to detect at least two-phase or more currents for respective said multi-system motor windings of said three-phase motor; three-phase/two-phase converting sections (320, 330) to convert said detected three-phase currents detected by said current detecting circuits (121A, 121B) to two-phase currents for respective said multi-system motor windings; and a failure diagnosing section (350, 310, 321, 331, 301, 302, 322, 332, 323, 333) to perform a current-calculation of said two-phase currents converted to two-phases by said three-phase/two-phase converting sections (320, 330) for respective said multi-system motor windings, and to perform a failure diagnosis characterized by the failure diagnosis being performed by respectively comparing a difference of current-calculated results between said multi-system motor windings and an accumulated value of said difference with respective failure-judgment thresholds; wherein said failure-judgment thresholds are determined based on said current command value, wherein in a case that said failure diagnosing section (350, 310, 321, 331, 301, 302, 322, 332, 323, 333) detects a failure, said failure diagnosing section (350, 310, 321, 331, 301, 302, 322, 332, 323, 333) judges a deviation in a continuous-driving capable value based on said failure-judgment thresholds and transmits a quantity of said deviation to a superior system or a superior controller so that drivings in multi-systems which include a failure system are successively continued. current detecting circuits (121A, 121B) to detect at least two-phase or more currents for respective said multi-system motor windings of said three-phase motor; three-phase/two-phase converting sections (320, 330) to convert said detected three-phase currents detected by said current detecting circuits (121A, 121B) to two-phase currents for respective said multi-system motor windings; and a failure diagnosing section (350, 310, 321, 331, 301, 302, 322, 332, 323, 333) to perform a current-calculation of said two-phase currents converted to two-phases by said three-phase/two-phase converting sections (320, 330) for respective said multi-system motor windings, and to perform a failure diagnosis characterized by the failure diagnosis being performed by respectively comparing a difference of current-calculated results between said multi-system motor windings and an accumulated value of said difference with respective failure-judgment thresholds; wherein said failure-judgment thresholds are determined based on said current command value, wherein in a case that said failure diagnosing section (350, 310, 321, 331, 301, 302, 322, 332, 323, 333) detects a failure, said failure diagnosing section (350, 310, 321, 331, 301, 302, 322, 332, 323, 333) judges a deviation in a continuous-driving capable value based on said failure-judgment thresholds and transmits a quantity of said deviation to a superior system or a superior controller so that drivings in multi-systems which include a failure system are successively continued.