A back light unit includes a lamp, a lamp house where the lamp is housed, a diffusion plate provided parallel to a main surface of the lamp house, a display part receiving light irradiated from the lamp and displaying, a frame member that has a structure in which the diffusion plate and the display part can be housed inside of the frame member and that detachably connects to the lamp house, and a shield member connected in a range from the diffusion plate to the frame member so that a space between the diffusion plate and the frame member is shielded.