An idling time period after applying a bias to a conversion element until a start of an accumulation of the conversion element for deriving an image and an accumulation period from the start of the accumulation to a termination of the accumulation are measured. An offset correction of the image is conducted by using a dark current accumulation charge quantity in the accumulation calculated based on the measured idling time period and accumulation period and stored dark current response characteristics. Thus, even just after applying the bias to the conversion element, the offset correction can be properly conducted. An imaging apparatus which can execute a good radiographing without increasing costs and a size even just after applying the bias to the conversion element is provided.