An imaging device according to one aspect of the present invention has a CCD, a mechanical shutter which prevents transmission of incident light beams to the CCD, a main CPU which sequentially reads stored electric charges obtained by the CCD in a plurality of field cycles and calculates a signal amplification rate based on an image signal which relies on the stored electric charge read to the last field of the plurality of field cycles, and a non-volatile memory which stores the signal amplification rate. The above-described calculation may be executed by an external PC.