A motor controlling device comprising: a high-side first switching element corresponding to each phase (U, V, W) of a three-phase brushless motor; a low-side second switching element corresponding to each phase (U, V, W); a shunt resistor disposed between and connected to the second switching element and a grounding line; a current value acquisition section for acquiring a value of a current flowing in the shunt resistor, a power controlling section for controlling the first switching element and the second switching element; and a decision section configured to obtain a value of a current flowing in the shunt resistor of each phase (U, V, W) and to effect an abnormality decision based on a sum of values of currents, the motor controlling device being characterized in that, when a duty ratio of the first switching element of any one phase (U,V,W) is found equal to or greater than a threshold value which is a value at which it is not possible to acquire a value of a current flowing in the shunt resistor of said phase, the decision section is further configured to use the power controlling section to perform control to switch OFF the first switching element of said phase for a predetermined period (Ta) during which it is possible to acquire a value of a current flowing in the shunt resistor of said phase, and also to switch ON the second switching element of said phase for the predetermined period (Ta), acquire a value of a current flowing in the shunt resistor of said phase, and also values of currents flowing in the shunt resistor of the other phases, and effect abnormality decision based on a sum of the values of currents, in at least one of the three-phase brushless motor, the first switching element, the second switching element the shunt resistor, the current value acquisition section, and the power controlling section. a high-side first switching element corresponding to each phase (U, V, W) of a three-phase brushless motor; a low-side second switching element corresponding to each phase (U, V, W); a shunt resistor disposed between and connected to the second switching element and a grounding line; a current value acquisition section for acquiring a value of a current flowing in the shunt resistor, a power controlling section for controlling the first switching element and the second switching element; and a decision section configured to obtain a value of a current flowing in the shunt resistor of each phase (U, V, W) and to effect an abnormality decision based on a sum of values of currents, the motor controlling device being characterized in that, when a duty ratio of the first switching element of any one phase (U,V,W) is found equal to or greater than a threshold value which is a value at which it is not possible to acquire a value of a current flowing in the shunt resistor of said phase, the decision section is further configured to use the power controlling section to perform control to switch OFF the first switching element of said phase for a predetermined period (Ta) during which it is possible to acquire a value of a current flowing in the shunt resistor of said phase, and also to switch ON the second switching element of said phase for the predetermined period (Ta), acquire a value of a current flowing in the shunt resistor of said phase, and also values of currents flowing in the shunt resistor of the other phases, and effect abnormality decision based on a sum of the values of currents, in at least one of the three-phase brushless motor, the first switching element, the second switching element the shunt resistor, the current value acquisition section, and the power controlling section.