In a refractive index measuring device (1) for measuring a refractive index of a solid sample (S), the solid sample (S) is closely attached to a prism (3) having a predetermined refractive index with a refractive index liquid (4) having a predetermined refractive index interposed therebetween. A scaled angle (light receiving member) (6) having a light receiving surface (6a) that receives first reflected light (R1), which is a part of light from a light source (2) and which is reflected by the prism (3), is provided. When the prism (3) is rotationally driven by a rotary table (rotational drive unit) (5) and an intensity of second reflected light (R2) detected by a detector (7) becomes lower than a predetermined value, the refractive index of the solid sample (S) is measured by using a position of the first reflected light (R1) on the light receiving surface (6a) of the scaled angle (6).