A radiography apparatus includes a conversion unit having conversion elements arranged in a row-column pattern. In an object-image reading operation, the conversion unit detects an object image based on illuminated radiations, and a drive circuit drives the conversion unit so as to allow the conversion unit to output a signal based on the object image. In an offset-data reading operation, the conversion unit detects offset data in a period when the radiations are not illuminating, and the drive circuit drives so as to allow the conversion unit to output a signal based on the offset data. When the numbers of lines driven concurrently in the object-image reading operation is represented by n (equal to 1 or greater) and the numbers of lines driven concurrently in offset-data reading operation is represented by m, the drive circuit controls the conversion unit so as to satisfy the expression: n