A toque motor driving device for wire cut electrical discharge machines that drives a torque motor using an AC power source, the toque motor driving device comprising: a bridge circuit connected between a rectification output of the full-wave rectifying circuit (11, 12, 13, 14) and the torque motor; characterised by a polarity determination signal generating circuit that detects a period during which an absolute value of a power voltage of the AC power source exceeds a first reference voltage in a period during which a polarity of the power voltage of the AC power source is positive and outputs a detection result as a first polarity determination signal (c) and detects a period during which the absolute value of the power voltage of the AC power source exceeds a second reference voltage in a period during which the polarity of the power voltage of the AC power source is negative; a PWM signal generating circuit that generates a PWM signal (e) whose duty is adjusted according to a physical quantity corresponding to a torque of the torque motor; and a logical AND circuit that obtains a logical AND between the PWM signal output from the PWM signal generating circuit and the first (c) and second (d) polarity determination signals output from the polarity determination signal generating circuit; wherein the bridge circuit includes a positive polarity switch group including two or more semiconductor switches (15, 18) that applies a positive voltage to the torque motor and a negative polarity switch group including two or more semiconductor switches (16, 17) that applies a negative voltage to the torque motor; wherein at least one of the semiconductor switches (15, 18) included in the positive polarity switch group operates according to a signal (g) of a logical AND between the first (c) or second (d) polarity determination signal and the PWM signal (e) and the other semiconductor switches operate according the first (c) or second (d) polarity determination signal wherein at least one of the semiconductor switches (16, 17) included in the negative polarity switch group operates according to a signal of a logical AND between the second (d) or first (c) polarity determination signal and the PWM signal (e) and the other semiconductor switches operate according the second (d) or first polarity determination signal (c). a bridge circuit connected between a rectification output of the full-wave rectifying circuit (11, 12, 13, 14) and the torque motor; characterised by a polarity determination signal generating circuit that detects a period during which an absolute value of a power voltage of the AC power source exceeds a first reference voltage in a period during which a polarity of the power voltage of the AC power source is positive and outputs a detection result as a first polarity determination signal (c) and detects a period during which the absolute value of the power voltage of the AC power source exceeds a second reference voltage in a period during which the polarity of the power voltage of the AC power source is negative; a PWM signal generating circuit that generates a PWM signal (e) whose duty is adjusted according to a physical quantity corresponding to a torque of the torque motor; and a logical AND circuit that obtains a logical AND between the PWM signal output from the PWM signal generating circuit and the first (c) and second (d) polarity determination signals output from the polarity determination signal generating circuit; wherein the bridge circuit includes a positive polarity switch group including two or more semiconductor switches (15, 18) that applies a positive voltage to the torque motor and a negative polarity switch group including two or more semiconductor switches (16, 17) that applies a negative voltage to the torque motor; wherein at least one of the semiconductor switches (15, 18) included in the positive polarity switch group operates according to a signal (g) of a logical AND between the first (c) or second (d) polarity determination signal and the PWM signal (e) and the other semiconductor switches operate according the first (c) or second (d) polarity determination signal wherein at least one of the semiconductor switches (16, 17) included in the negative polarity switch group operates according to a signal of a logical AND between the second (d) or first (c) polarity determination signal and the PWM signal (e) and the other semiconductor switches operate according the second (d) or first polarity determination signal (c).