To provide an imaging apparatus capable of reading image signals at effective timings and updating displaying without needlessly increasing the read-out times of the image signals from an imaging device.

Image signals are read from an imaging device at a first timing and a second timing during long exposure (S11). The image signal read at the first timing is added to the image signal read at the second timing, so as to display an addition image (S13, S17). The image signals read at the first and second timings are compared so as to evaluate existence of a spatial change (S15). The read-out period of the image signals is determined based on the evaluation result (S19).