1. An endoscope apparatus comprising: an observation optical system; a solid-state imaging element that is relatively positioned and fixed with respect to the observation optical system, obtains an optical image formed thereon by the observation optical system, and has a plurality of photoelectric conversion elements arrayed therein which photoelectrically convert the optical image; a memory section that stores image cutting-out information therein that specifies an image cutting-out region for a process of cutting out an image for display, which corresponds to a display area to be displayed on a monitor, from an image generated on the basis of an imaging signal of the solid-state imaging element; a processor configured to perform steps of: obtaining the image cutting-out region, from an overlapping region in which a displayable pixel area of the solid-state imaging element and an imaging area of the optical image to be formed on the solid-state imaging element by the observation optical system overlap one another, where the center of the imaging area is matched with the center of the display area; storing in the memory section the image cutting-out information based on the image cutting-out region; cutting out an image for display based on the cutting-out information stored in the memory section; expanding the image for display to an image size of the display area, when an image size of the cut-out image for display becomes smaller than the image size of the display area due to deviation between the center of the displayable pixel area and the center of the imaging area.