A radiation imaging apparatus comprising: a plurality of pixels arranged in an array, each pixel including a conversion element (C11 - C33) configured to convert radiation into charge and a switching element (T11 - T33) configured to transfer an electrical signal based on the charge during a conductive state; a plurality of first lines (Dr1 - Dr3) respectively connected to different lines of the switching elements; a circuit configured to repeat a reset operation of resetting the conversion elements by switching a signal applied to one or more of the plurality of first lines from a non-conductive voltage to a conductive voltage and then returning the signal to the non-conductive voltage, such that the reset operation is performed for each first line during one frame, wherein the conductive voltage is configured to set the switching elements in a conductive state and the non-conductive voltage is configured to set the switching elements in a non-conductive state; and a second line (Bs1 - Bs3, BsC) for applying bias voltage to the conversion elements of the plurality of pixels to make the conversion elements convert radiation into charge, characterized by: an acquisition means configured to repeatedly acquire values based on a current flowing in the second line while the reset operation is performed; and a determination means configured to compare an amount of change between a first value and a second value with a threshold value to determine whether radiation has been irradiated onto the conversion element, the first value being acquired by the acquisition means and the second value being based on one or more values acquired by the acquisition means in a frame prior to another frame in which the first value is acquired, the one or more values having been acquired in a state in which radiation has not been irradiated onto the conversion element. a plurality of pixels arranged in an array, each pixel including a conversion element (C11 - C33) configured to convert radiation into charge and a switching element (T11 - T33) configured to transfer an electrical signal based on the charge during a conductive state; a plurality of first lines (Dr1 - Dr3) respectively connected to different lines of the switching elements; a circuit configured to repeat a reset operation of resetting the conversion elements by switching a signal applied to one or more of the plurality of first lines from a non-conductive voltage to a conductive voltage and then returning the signal to the non-conductive voltage, such that the reset operation is performed for each first line during one frame, wherein the conductive voltage is configured to set the switching elements in a conductive state and the non-conductive voltage is configured to set the switching elements in a non-conductive state; and a second line (Bs1 - Bs3, BsC) for applying bias voltage to the conversion elements of the plurality of pixels to make the conversion elements convert radiation into charge, characterized by: an acquisition means configured to repeatedly acquire values based on a current flowing in the second line while the reset operation is performed; and a determination means configured to compare an amount of change between a first value and a second value with a threshold value to determine whether radiation has been irradiated onto the conversion element, the first value being acquired by the acquisition means and the second value being based on one or more values acquired by the acquisition means in a frame prior to another frame in which the first value is acquired, the one or more values having been acquired in a state in which radiation has not been irradiated onto the conversion element. an acquisition means configured to repeatedly acquire values based on a current flowing in the second line while the reset operation is performed; and a determination means configured to compare an amount of change between a first value and a second value with a threshold value to determine whether radiation has been irradiated onto the conversion element, the first value being acquired by the acquisition means and the second value being based on one or more values acquired by the acquisition means in a frame prior to another frame in which the first value is acquired, the one or more values having been acquired in a state in which radiation has not been irradiated onto the conversion element.