A radiation imaging apparatus (100, 1800, 1900) comprising: a pixel array having a plurality of pixels arranged in a plurality of rows and a plurality of columns, each pixel including a conversion element for accumulating charge in accordance with radiation and a switching element for connecting the conversion element to a signal line (Sig); a bias line (Vs) for supplying a bias potential to the conversion elements of the plurality of pixels; a plurality of driving lines for supplying a driving signal to control the switching elements of the plurality of pixels; a driving means for supplying a driving signal to the plurality of driving lines in units of one or more driving lines and repeating an initialization operation that is performed in each driving cycle, the initialization operation comprising switching each driving signal from an OFF voltage at which the switching element is turned off, to an ON voltage at which the switching element is turned on, and then returning the driving signal to the OFF voltage, the driving cycle being a time duration from the time when a driving signal to a particular one of the units of one or more driving lines is switched to the ON voltage to the time when a driving signal to a next one of the units of one or more driving lines is switched to the ON voltage; an acquisition means arranged to acquire a plurality of signal values, each signal value representing a current flowing through said bias line; a calculation means arranged to calculate radiation information based on the plurality of signal values; and a determination means arranged to determine whether irradiation of said pixel array with radiation is present based on the radiation information calculated by the calculation means; wherein said acquisition means is arranged to acquire, as an effective value, a signal value of the plurality of signal values representing a current flowing through said bias line upon supply of the ON voltage to one of the units of one or more driving lines, and acquire, as a noise value, a signal value of the plurality of signal values representing a current flowing through said bias line upon supply of the OFF voltage to each of the units of one or more driving lines, and said calculation means is arranged to calculate the radiation information based on the effective value and the noise value. a pixel array having a plurality of pixels arranged in a plurality of rows and a plurality of columns, each pixel including a conversion element for accumulating charge in accordance with radiation and a switching element for connecting the conversion element to a signal line (Sig); a bias line (Vs) for supplying a bias potential to the conversion elements of the plurality of pixels; a plurality of driving lines for supplying a driving signal to control the switching elements of the plurality of pixels; a driving means for supplying a driving signal to the plurality of driving lines in units of one or more driving lines and repeating an initialization operation that is performed in each driving cycle, the initialization operation comprising switching each driving signal from an OFF voltage at which the switching element is turned off, to an ON voltage at which the switching element is turned on, and then returning the driving signal to the OFF voltage, the driving cycle being a time duration from the time when a driving signal to a particular one of the units of one or more driving lines is switched to the ON voltage to the time when a driving signal to a next one of the units of one or more driving lines is switched to the ON voltage; an acquisition means arranged to acquire a plurality of signal values, each signal value representing a current flowing through said bias line; a calculation means arranged to calculate radiation information based on the plurality of signal values; and a determination means arranged to determine whether irradiation of said pixel array with radiation is present based on the radiation information calculated by the calculation means; wherein said acquisition means is arranged to acquire, as an effective value, a signal value of the plurality of signal values representing a current flowing through said bias line upon supply of the ON voltage to one of the units of one or more driving lines, and acquire, as a noise value, a signal value of the plurality of signal values representing a current flowing through said bias line upon supply of the OFF voltage to each of the units of one or more driving lines, and said calculation means is arranged to calculate the radiation information based on the effective value and the noise value.