A measuring instrument includes a light source, a dial plate with a scale design, and a light guide member. The light guide member includes a receiving portion for receiving the light from the light source, and a flat plate portion for irradiating the light transmitted from the receiving portion to the dial plate. The flat plane portion includes a thick wall section located close to the scale design, and a thin wall section extending from the thick wall section in a direction away from the light source. The thick wall section is thicker than the thick wall section. A boundary end face connected to a region of the thick wall section and a region of the thin wall section in the second face of the light guide member reflects the light transmitted in the light guide member from the light receiving portion to irradiate the image design.