A thyristor starter configured to start a synchronous machine, comprising: a converter that converts AC power into DC power; a DC reactor that smoothes the DC power; an inverter that converts the DC power applied from the converter through the DC reactor into AC power with a variable frequency and supplies the AC power to the synchronous machine; a position detector that detects a rotor position of the synchronous machine; a first controller that controls a firing phase of a thyristor in the inverter, based on a detection signal of the position detector; and a second controller that controls a firing phase of a thyristor in the converter such that DC current flowing through the DC reactor matches a current command value, based on a detection signal of the position detector, wherein the thyristor starter accelerates the synchronous machine from a stop state to a predetermined rotation speed by successively performing a first mode of performing commutation of the inverter by intermittently setting the DC current to zero and a second mode of performing commutation of the inverter by induced voltage of the synchronous machine, characterized in that the second controller includes a current controller at least including an integral element integrating a deviation of the DC current from the current command value, the current controller generates a voltage command value of output voltage of the converter by performing control calculation of the deviation, and a control angle calculator that calculates a phase control angle of a thyristor in the converter, based on the voltage command value, in the first mode, the control angle calculator sets the DC current to zero for a predetermined pause time by narrowing the phase control angle simultaneously with a commutation command for the inverter, and in the first mode, when the control calculation is resumed immediately after the pause time, the current controller uses a control amount calculated by the control calculation immediately before the pause time as a preset value of the integral element immediately after the pause time. a converter that converts AC power into DC power; a DC reactor that smoothes the DC power; an inverter that converts the DC power applied from the converter through the DC reactor into AC power with a variable frequency and supplies the AC power to the synchronous machine; a position detector that detects a rotor position of the synchronous machine; a first controller that controls a firing phase of a thyristor in the inverter, based on a detection signal of the position detector; and a second controller that controls a firing phase of a thyristor in the converter such that DC current flowing through the DC reactor matches a current command value, based on a detection signal of the position detector, wherein the thyristor starter accelerates the synchronous machine from a stop state to a predetermined rotation speed by successively performing a first mode of performing commutation of the inverter by intermittently setting the DC current to zero and a second mode of performing commutation of the inverter by induced voltage of the synchronous machine, characterized in that the second controller includes a current controller at least including an integral element integrating a deviation of the DC current from the current command value, the current controller generates a voltage command value of output voltage of the converter by performing control calculation of the deviation, and a control angle calculator that calculates a phase control angle of a thyristor in the converter, based on the voltage command value, characterized in that the second controller includes a current controller at least including an integral element integrating a deviation of the DC current from the current command value, the current controller generates a voltage command value of output voltage of the converter by performing control calculation of the deviation, and a control angle calculator that calculates a phase control angle of a thyristor in the converter, based on the voltage command value, in the first mode, the control angle calculator sets the DC current to zero for a predetermined pause time by narrowing the phase control angle simultaneously with a commutation command for the inverter, and in the first mode, when the control calculation is resumed immediately after the pause time, the current controller uses a control amount calculated by the control calculation immediately before the pause time as a preset value of the integral element immediately after the pause time.