A thyristor starting device, comprising: a converter configured to convert AC power supplied from an AC power source into DC power; a DC reactor configured to smooth a DC current (Id); an inverter configured to convert the DC power provided from said converter through said DC reactor into AC power, and to supply the AC power to a synchronous machine; a gate pulse generation circuit configured to generate a gate pulse to be provided to thyristors of said converter and said inverter; a control unit configured to set a phase control angle (α) of the gate pulse to be provided to the thyristors of said converter, by controlling a current of said converter such that the DC current flowing into said DC reactor matches a current command value (Id*); and an abnormality detection unit comprising a timer, the abnormality detection unit configured to set an upper limit value and a lower limit value of an acceptable range on a high-current side and a low-current side, respectively, relative to said current command value, to compare a detection value of the DC current (Id) with said upper limit value and lower limit value, and in response to the DC current (Id) flowing into said DC reactor deviating from said acceptable range, to provide a signal to the timer; wherein the timer is configured to measure a time for which the signal is received, and the timer is reset when the signal stops; wherein the abnormality detection unit is configured to determine an abnormality in said gate pulse when the measured time reaches a prescribed time; wherein the abnormality detection unit invalidates abnormality determination for a fixed time (Tst) after energization of the thyristor starting device is started, in order to prevent an overshoot in the DC current (Id) from being erroneously determined as an abnormality in the gate pulse when the current command value (Id*) changes suddenly from zero. a converter configured to convert AC power supplied from an AC power source into DC power; a DC reactor configured to smooth a DC current (Id); an inverter configured to convert the DC power provided from said converter through said DC reactor into AC power, and to supply the AC power to a synchronous machine; a gate pulse generation circuit configured to generate a gate pulse to be provided to thyristors of said converter and said inverter; a control unit configured to set a phase control angle (α) of the gate pulse to be provided to the thyristors of said converter, by controlling a current of said converter such that the DC current flowing into said DC reactor matches a current command value (Id*); and an abnormality detection unit comprising a timer, the abnormality detection unit configured to set an upper limit value and a lower limit value of an acceptable range on a high-current side and a low-current side, respectively, relative to said current command value, to compare a detection value of the DC current (Id) with said upper limit value and lower limit value, and in response to the DC current (Id) flowing into said DC reactor deviating from said acceptable range, to provide a signal to the timer; wherein the timer is configured to measure a time for which the signal is received, and the timer is reset when the signal stops; wherein the abnormality detection unit is configured to determine an abnormality in said gate pulse when the measured time reaches a prescribed time; wherein the abnormality detection unit invalidates abnormality determination for a fixed time (Tst) after energization of the thyristor starting device is started, in order to prevent an overshoot in the DC current (Id) from being erroneously determined as an abnormality in the gate pulse when the current command value (Id*) changes suddenly from zero.