A driving controller (10A; 10B) for an AC motor comprising: an inverter that includes a plurality of on-off controlled switching elements (UP, VP, WP, VN, UN, WN) and converts a DC voltage into an AC voltage with an arbitrary frequency to drive the AC motor; and a motor side switch connected between the inverter and the AC motor, characterized in that the driving controller further comprises: an electric-quantity detector (13, 14, 15) that detects an electric quantity at an output side of the inverter; and a control unit (17A; 17B) that on-off controls the switching elements (UP, VP, WP, VN, UN, WN) in the inverter and controls the motor side switch to open and close based on at least a current detected by the electric-quantity detector (13, 14, 15), wherein the control unit (17A; 17B) comprises: a current-state determining unit that generates a determination signal indicating whether a current detected by the electric-quantity detector (13, 14, 15) is in an abnormal state; and a contactor control unit (40A; 40B) that controls based on the determination signal a timing of actually outputting an instruction, which has been generated for opening the motor side switch, to the motor side switch, the driving controller (10A; 10B) further comprises: a discharging circuit connected in parallel to a capacitor provided between a positive side conductor and a negative side conductor of the inverter, to which the DC voltage is applied, and the discharging circuit is controlled to discharge electric charges of the capacitor before the motor side switch is opened. an inverter that includes a plurality of on-off controlled switching elements (UP, VP, WP, VN, UN, WN) and converts a DC voltage into an AC voltage with an arbitrary frequency to drive the AC motor; and a motor side switch connected between the inverter and the AC motor, characterized in that the driving controller further comprises: an electric-quantity detector (13, 14, 15) that detects an electric quantity at an output side of the inverter; and a control unit (17A; 17B) that on-off controls the switching elements (UP, VP, WP, VN, UN, WN) in the inverter and controls the motor side switch to open and close based on at least a current detected by the electric-quantity detector (13, 14, 15), wherein the control unit (17A; 17B) comprises: a current-state determining unit that generates a determination signal indicating whether a current detected by the electric-quantity detector (13, 14, 15) is in an abnormal state; and a contactor control unit (40A; 40B) that controls based on the determination signal a timing of actually outputting an instruction, which has been generated for opening the motor side switch, to the motor side switch, the driving controller (10A; 10B) further comprises: a discharging circuit connected in parallel to a capacitor provided between a positive side conductor and a negative side conductor of the inverter, to which the DC voltage is applied, and the discharging circuit is controlled to discharge electric charges of the capacitor before the motor side switch is opened. an electric-quantity detector (13, 14, 15) that detects an electric quantity at an output side of the inverter; and a control unit (17A; 17B) that on-off controls the switching elements (UP, VP, WP, VN, UN, WN) in the inverter and controls the motor side switch to open and close based on at least a current detected by the electric-quantity detector (13, 14, 15), wherein the control unit (17A; 17B) comprises: a current-state determining unit that generates a determination signal indicating whether a current detected by the electric-quantity detector (13, 14, 15) is in an abnormal state; and a contactor control unit (40A; 40B) that controls based on the determination signal a timing of actually outputting an instruction, which has been generated for opening the motor side switch, to the motor side switch, a current-state determining unit that generates a determination signal indicating whether a current detected by the electric-quantity detector (13, 14, 15) is in an abnormal state; and a contactor control unit (40A; 40B) that controls based on the determination signal a timing of actually outputting an instruction, which has been generated for opening the motor side switch, to the motor side switch, the driving controller (10A; 10B) further comprises: a discharging circuit connected in parallel to a capacitor provided between a positive side conductor and a negative side conductor of the inverter, to which the DC voltage is applied, and the discharging circuit is controlled to discharge electric charges of the capacitor before the motor side switch is opened. a discharging circuit connected in parallel to a capacitor provided between a positive side conductor and a negative side conductor of the inverter, to which the DC voltage is applied, and the discharging circuit is controlled to discharge electric charges of the capacitor before the motor side switch is opened.