A radiation imaging system includes pixel array, scanning circuit to scan rows of the pixel array, and readout circuit to read signals from the pixel array. Each pixel includes converter to generate electric signal corresponding to radiation and transistor connected to the converter. The readout circuit reads signal from the converter via the transistor. The system performs image capturing modes and conditioning mode of conditioning a threshold voltage of the transistor. In the conditioning mode, the scanning circuit supplies, to a gate of the transistor, an OFF voltage different from OFF voltages in the image capturing modes. The scanning circuit scans the rows in units of at least one row in the image capturing modes, and scans the rows in units of at least two rows in the conditioning mode.
