A thyristor starter that starts a synchronous machine, the thyristor starter 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 detector (5, 6) that detects AC current and AC voltage supplied to the synchronous machine from the inverter; a position detector that detects a position of a rotor of the synchronous machine based on a signal from the detector (5, 6); and a controller that controls a firing phase of the inverter, wherein the thyristor starter accelerates the synchronous machine from a stop state to a predetermined rotation speed by sequentially performing a first mode and a second mode, the thyristor starter performing, in the first mode, commutation of the inverter by intermittently setting DC output current (Id) of the converter to zero, the thyristor starter performing, in the second mode, commutation of the inverter by induced voltage of the synchronous machine, characterized in that the controller includes: a control angle calculator that calculates a rotation speed of the synchronous machine based on a signal from the position detector and calculates a firing angle (γ) of the inverter based on the calculated rotation speed of the synchronous machine, and a gate pulse generator that generates a firing command to be applied to the inverter based on the firing angle (γ) received from the control angle calculator, and during a first time period from start of performance of the second mode to arrival of the induced voltage at a first voltage value, the firing angle (γ) of the inverter is changed such that a value thereof becomes larger as the rotation speed of the synchronous machine becomes higher. 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 detector (5, 6) that detects AC current and AC voltage supplied to the synchronous machine from the inverter; a position detector that detects a position of a rotor of the synchronous machine based on a signal from the detector (5, 6); and a controller that controls a firing phase of the inverter, wherein the thyristor starter accelerates the synchronous machine from a stop state to a predetermined rotation speed by sequentially performing a first mode and a second mode, the thyristor starter performing, in the first mode, commutation of the inverter by intermittently setting DC output current (Id) of the converter to zero, the thyristor starter performing, in the second mode, commutation of the inverter by induced voltage of the synchronous machine, characterized in that the controller includes: a control angle calculator that calculates a rotation speed of the synchronous machine based on a signal from the position detector and calculates a firing angle (γ) of the inverter based on the calculated rotation speed of the synchronous machine, and a gate pulse generator that generates a firing command to be applied to the inverter based on the firing angle (γ) received from the control angle calculator, and a control angle calculator that calculates a rotation speed of the synchronous machine based on a signal from the position detector and calculates a firing angle (γ) of the inverter based on the calculated rotation speed of the synchronous machine, and a gate pulse generator that generates a firing command to be applied to the inverter based on the firing angle (γ) received from the control angle calculator, and during a first time period from start of performance of the second mode to arrival of the induced voltage at a first voltage value, the firing angle (γ) of the inverter is changed such that a value thereof becomes larger as the rotation speed of the synchronous machine becomes higher.