A light or radiation image pickup apparatus comprises a first arithmetic unit 50 for calculating a first arithmetic value by subtracting a first offset signal from a main signal, a second arithmetic unit 51 for calculating a second arithmetic value which is a difference between a second offset signal and the first offset signal, and a correcting unit 52 for correcting the first arithmetic value calculated by the first arithmetic unit 50, by using the second arithmetic value calculated by the second arithmetic unit 51 and corresponding to a period of the same length as a period from the first offset signal to the main signal used in the operation in the first arithmetic unit 50. The first arithmetic value is corrected to remove noise components due to leakage of charge signals accumulated during the period from the first offset signal to the main signal. It is thus possible to reduce deterioration of image quality due to leaks of charge signals accumulated in X-ray detecting elements 11 (leakage currents) and prevent an extended imaging time.