A depth expansion apparatus includes an image-pickup-optical-system and an image-pickup-device (hereinafter, IPS) configured to form and pick up images A and B in different focus positions, and a depth-expanded-image forming section configured to generate, based on the images A and B, a depth-expanded-image that maintains a relation between a distance from an object point to the image-pickup-optical-system and luminance. When an image side NA of the image A is represented as NA′, a resolution determined by the IPS, as R, an optical path interval between image forming surfaces for the images A and B, as d, NA of an image at a near photographing distance among the images A and B, as NAn, and NA of an image at a far photographing distance among the images A and B, as NAf, the IPS satisfy the following conditional expressions (1) and (2): R×NA′/2≦d  (1) 0.05≦(NAf/NAn)2≦0.9  (2).