An image generation device generates a plurality of reference in-focus images of an object placed on a surface of an image sensor by using a plurality of images captured by the image sensor using sensor pixels when the object is irradiated with light by a plurality of illuminators. Each of the reference in-focus images is an in-focus image corresponding to one of a plurality of virtual reference focal planes that are located between the image sensor and the plurality of illuminators. The plurality of reference focal planes pass through the object and are spaced apart from one another. The image generation device generates a three-dimensional image of the object by using the reference in-focus images and displays the three-dimensional image on a display screen.