A multiphase motor driving device has an inverter circuit. The inverter circuit includes a pair of upper and lower switching elements, a shunt resistor for phase current detection, and a voltage for driving a multiphase motor. The device includes a determination unit for shifting a detection timing of the current flowing to the shunt resistor from the OFF period to the ON period of the switching element on the upper side in the phase. The determination unit determines whether or not ON failure occurs based on the current flowing to the shunt resistor of the phase in the ON period. The device has a current value estimation unit for estimating a current value of the phase in a case where the detection timing is shifted based on currents flowing to the shunt resistors of other phases.