A motor control device comprising control means for outputting a motor control signal and a drive circuit formed by connecting pairs of serially connected switching elements (7a, 7b, 7c, 7d, 7e, 7f) in parallel so that each switching element (7a, 7b, 7c, 7d, 7e, 7f) is turned on or off on the basis of the motor control signal, to thereby convert a direct current power into a drive power of three phases, which is then supplied to a motor, wherein the control means is configured to generate the motor control signal in order to supply the drive power through an energization with rectangular waves for switching an energized phase and the direction of the energization for every predetermined electrical angle of the motor, and is configured to carry out a PWM control on each switching element ( 7d, 7e, 7f) on the grounded side to thereby control the voltage applied to the motor, the motor control device comprising: voltage detection means ( 13u, 13v, 13w) for detecting each phase voltage ( Vu, Vv, Vw) of the motor; and break detection means for detecting a break in a power supply line ( Lp_u, Lp_v, Lp_w) corresponding to each phase on the basis of each detected phase voltage, characterized in that the break detection means is configured to determine that at least one of the power supply lines ( Lp_u, Lp_v, Lp_w) is broken in the case where a low voltage being the lowest voltage of the detected phase voltages is lower than a predetermined voltage ( Vth) set in the vicinity of the grounded voltage, and is further configured to determine that two of the power supply lines ( Lp_u, Lp_v, Lp_w) are broken in the case where a middle voltage, which is a middle voltage of the phase voltages between a highest voltage of the detected phase voltages and the low voltage, is lower than the predetermined voltage ( Vth), wherein the break detection means has a counter for adding a predetermined value at every detection of a break and the break detection means is further configured to determine the detection of a break on the basis of the comparison of the low voltage and middle voltage to the predetermined voltage (Vth) for every predetermined period, wherein, when the accumulated value of the counter becomes a predetermined threshold value or higher, the break detection means is configured to determine the detection of a break in the power supply line ( Lp_u, Lp_v, Lp_w), and wherein, as the predetermined value to be added, the value in the case where two breaks of the power supply lines (Lp_u, Lp_v, Lp_w) are detected is set to be greater than the value in the case where at least one break is detected. voltage detection means ( 13u, 13v, 13w) for detecting each phase voltage ( Vu, Vv, Vw) of the motor; and break detection means for detecting a break in a power supply line ( Lp_u, Lp_v, Lp_w) corresponding to each phase on the basis of each detected phase voltage, characterized in that the break detection means is configured to determine that at least one of the power supply lines ( Lp_u, Lp_v, Lp_w) is broken in the case where a low voltage being the lowest voltage of the detected phase voltages is lower than a predetermined voltage ( Vth) set in the vicinity of the grounded voltage, and is further configured to determine that two of the power supply lines ( Lp_u, Lp_v, Lp_w) are broken in the case where a middle voltage, which is a middle voltage of the phase voltages between a highest voltage of the detected phase voltages and the low voltage, is lower than the predetermined voltage ( Vth), wherein the break detection means has a counter for adding a predetermined value at every detection of a break and the break detection means is further configured to determine the detection of a break on the basis of the comparison of the low voltage and middle voltage to the predetermined voltage (Vth) for every predetermined period, wherein, when the accumulated value of the counter becomes a predetermined threshold value or higher, the break detection means is configured to determine the detection of a break in the power supply line ( Lp_u, Lp_v, Lp_w), and wherein, as the predetermined value to be added, the value in the case where two breaks of the power supply lines (Lp_u, Lp_v, Lp_w) are detected is set to be greater than the value in the case where at least one break is detected.