A radiation image pickup apparatus capable of setting an optimum threshold value used for instantaneously and highly accurately detecting the presence/absence of irradiation includes a pixel array having a plurality of pixels arranged in a matrix, where each of the pixels includes a conversion element and a switch element, a drive circuit for supplying a drive signal for controlling the switch element between a conducting state and a non-conducting state, a detection unit for outputting a detection signal varying with the intensity of irradiation of the pixel array, and an arithmetic unit for calculating an end threshold value used to detect end of irradiation on the basis of the signal output from the detection unit during a period of time during which irradiation is applied to the pixel array in which the switch elements of the pixels are set in a non-conducting state by the drive circuit.
