A radiation imaging apparatus comprising: an image sensor comprising a plurality of pixel circuits that are two dimensionally arrayed to perform imaging operation, each of which comprises a photoelectric conversion element and outputs an analog pixel signal corresponding to radiation irradiated during accumulation time; scanning means (303, 304) configured to scan the plurality of pixel circuits to extract an analog pixel signal therefrom; characterized in that the radiation imaging apparatus further comprises: a correction circuit (411-418, 431-438) comprising a D/A converter configured to convert an inputted digital value into an analog correction value and an adder to obtain the sum of said analog correction value and an inputted analog signal and to supply said sum to an A/D converter; and control means configured to: obtain a target value before the imaging operation by sampling a predetermined number of N of digital data DAn at the output of the A/D converter while supplying an analog reference voltage signal (Vref) and a digital reference value of ±0 to the correction circuit, and by summing said predetermined number N of digital data DAn into a target value ΣDAn; obtain a digital correction data DCn after the accumulation time of each frame by sampling a predetermined number N' of digital data DBn at the output of the A/D converter while supplying said analog reference voltage signal and said digital reference value of ±0 to the correction circuit, and by calculating DCn as a difference between the average ∑DAn/N of the digital data DAn and an average ∑DBn/N' of the digital data DBn; execute a control of scanning of the plurality of pixel circuits by the scanning means (303, 304) to readout pixel data while supplying the extracted analog pixel signal and the digital correction data DCn to the correction circuit; thereby reducing an offset generated by 1/f noise in the A/D converter and superimposed on the converted digital image data. an image sensor comprising a plurality of pixel circuits that are two dimensionally arrayed to perform imaging operation, each of which comprises a photoelectric conversion element and outputs an analog pixel signal corresponding to radiation irradiated during accumulation time; scanning means (303, 304) configured to scan the plurality of pixel circuits to extract an analog pixel signal therefrom; characterized in that the radiation imaging apparatus further comprises: a correction circuit (411-418, 431-438) comprising a D/A converter configured to convert an inputted digital value into an analog correction value and an adder to obtain the sum of said analog correction value and an inputted analog signal and to supply said sum to an A/D converter; and control means configured to: obtain a target value before the imaging operation by sampling a predetermined number of N of digital data DAn at the output of the A/D converter while supplying an analog reference voltage signal (Vref) and a digital reference value of ±0 to the correction circuit, and by summing said predetermined number N of digital data DAn into a target value ΣDAn; obtain a digital correction data DCn after the accumulation time of each frame by sampling a predetermined number N' of digital data DBn at the output of the A/D converter while supplying said analog reference voltage signal and said digital reference value of ±0 to the correction circuit, and by calculating DCn as a difference between the average ∑DAn/N of the digital data DAn and an average ∑DBn/N' of the digital data DBn; execute a control of scanning of the plurality of pixel circuits by the scanning means (303, 304) to readout pixel data while supplying the extracted analog pixel signal and the digital correction data DCn to the correction circuit; thereby reducing an offset generated by 1/f noise in the A/D converter and superimposed on the converted digital image data. obtain a target value before the imaging operation by sampling a predetermined number of N of digital data DAn at the output of the A/D converter while supplying an analog reference voltage signal (Vref) and a digital reference value of ±0 to the correction circuit, and by summing said predetermined number N of digital data DAn into a target value ΣDAn; obtain a digital correction data DCn after the accumulation time of each frame by sampling a predetermined number N' of digital data DBn at the output of the A/D converter while supplying said analog reference voltage signal and said digital reference value of ±0 to the correction circuit, and by calculating DCn as a difference between the average ∑DAn/N of the digital data DAn and an average ∑DBn/N' of the digital data DBn; execute a control of scanning of the plurality of pixel circuits by the scanning means (303, 304) to readout pixel data while supplying the extracted analog pixel signal and the digital correction data DCn to the correction circuit; thereby reducing an offset generated by 1/f noise in the A/D converter and superimposed on the converted digital image data.