1. An image processing device comprising: an image frame determination unit configured to determine, from image frames acquired through imaging at different imaging rates, image frames imaged at at least one of the different imaging rates to be image frames for which a displaying rate is to be changed; and a displaying rate adjustment unit configured to adjust the displaying rate of the image frames, determined to be the image frames for which the displaying rate is to be changed by the image frame determination unit, within a predetermined period from a timing when the imaging rate is switched.