1. An image capturing device comprising: a housing; a reference pattern used for color measurement, the reference pattern being arranged in the housing; an image capturing element that captures an image of the reference pattern in a first area of an image capturing area and an image of an object in a second area of the image capturing area; an image forming element that causes the image of the reference pattern and the image of the object to be formed on the image capturing element, the image forming element being arranged on a first optical path between the image capturing element and the reference pattern and a second optical path between the image capturing element and the object; and an optical member that guides any one of the image of the reference pattern and the image of the object so that the image of the object formed by the image forming element and the image of the reference pattern formed by the image forming element are to be formed on an element surface of the image capturing element.