Provided is a radiation imaging apparatus including: a conversion unit including a plurality of pixels arranged two-dimensionally, wherein each of the pixels includes a conversion element for converting incident radiation into an electric charge and a switching element for transferring an electric signal based on the electric charge; a drive circuit unit for outputting, to the switching element, a drive signal having a voltage for turning on the switching element; a read-out circuit unit for reading out the electric signal from the pixel; a calculating unit for calculating the S/N ratio of the electric signal read out by the read-out circuit unit; and a determination unit capable of changing the voltage of the drive signal output from the drive circuit unit according to the S/N ratio calculated. As a result, the radiation imaging apparatus capable of improving the S/N ratio of the derived image is provided.