There is provided a transmissive dimension measuring device in which a user can intuitively and easily adjust optical axes of a projector and an optical receiver, and in which a suitable action can be immediately taken when contamination is attached to a light projecting surface of the projector and a light receiving surface of the optical receiver. An incident light position display unit provided on the optical receiver expresses a light projecting spot in a pseudo manner by making an LED corresponding to an incident light position turn on, the light projecting spot being incident on the optical receiver arranged with a predetermined interval to the projector which projects light. The incident light position display unit is provided on an upper surface side opposite to a bottom surface that is a surface on which the optical receiver is installed on a base.