An illuminating device includes a linear light source mounted on a mounting surface of a board, with a plurality of light-emitting elements being arrayed thereon, for irradiating light toward an illuminating target, a white reflecting surface provided in a planar shape parallel to an optical axis of the linear light source on a surface including the mounting surface, to reflect the light from the linear light source, and a mirror surface formed in a planar shape that reflects the light from the linear light source and reflected light from the white reflecting surface. The linear light source, the white reflecting surface, and the mirror surface are arranged such that a third plane crosses a first plane on the illuminating target side than a second plane, and 0°