PURPOSE: To eliminate the spatial restriction of a measuring sample during the measurement of reflectance without significant alteration of two luminous flux formation systems, by positioning the measuring sample behind a reference sample in the incident direction of a luminous flux in such a manner as not to contact the reference sample.

CONSTITUTION: In a double-beam type ultraviolet, visible light spectrophotometer or the like a reflector M1 reflects a luminous flux R on the side of a reference optical path so as to be incident on a reference sample MR at a specified angle of incidence. A reflector M2 reflects the luminous flux reflected from the sample MR so as to be incident on a detector along the extension of the luminous flux R incident on the reflector M1. A reflector M3 reflects a luminous flux S on the side of the optical path of the sample so as to be incident on a measuring sample MS at a specified angle of incidence the same as that of the luminous flux R into the sample MR. A reflector M4 reflects the luminous flux reflected from the sample MS so as to be incident on the detector along the extension of the luminous flux S incident on the reflector M3. Then, the interval between the reflectors M3 and M4 is made so larger than the interval between the reflectors M1 and M2 as to place the sample MS behind the sample MR thereby making the angle of incidence on the sample in the manner that both of the optical paths are equal to each other.