1. An image capturing unit comprising: a housing including a surface facing a subject that is outside the image capturing unit; a board facing a back of the surface; a sensor, disposed with respect to the board so as to face the back of the surface, that image-captures a predetermined area including the subject; a reference chart that is arranged in the housing and is captured with the subject by the sensor; and an illumination light source that illuminates the subject and the reference chart, wherein the surface includes an opening, and the illumination light source is disposed on the board such that its projected position perpendicularly from the board onto the surface is between the reference chart and the opening.