1. An imaging device comprising: a movable stage capable of moving in two different directions while mounting an object to be inspected; a camera which is arranged in face-to-face relation to the movable stage, photographs the object to be inspected, and generates a moving picture image made of a plurality of sequential frame images; a mosaic image generation unit which assembles not less than two still images photographed by the camera, and generates a mosaic image that is wider in field of view than the actual field of view of the camera; a relative position determination unit which determines a relative position between the frame image and the mosaic image; a display reduction unit which reduces the frame image and the mosaic image respectively based on the image size of the mosaic image, and generates a display frame image and a display mosaic image; and a live image display unit which updates a display position of the display frame image with respect to the display mosaic image based on a determination result of the relative position, and displays a moving picture image configured by the display frame images on the display mosaic image.