The CPU 120 acquires zoom level sent by the zoom lens position detector 122, and on the basis of the acquired zoom level calculates a exposure target value depending on the particular zoom level. The CPU 120 establishes in the imaging controller 105 an exposure target value R calculated depending on zoom level Z, and issues an imaging command to the imaging controller 105. By so doing, the average value of gradation values of the white portion in the imaged image can be substantially maintained at the desired tone level.