[Object]To obtain interference light having a stronger light intensity, and to more accurately measure a refractive index of a measured object, with a simplified configuration.[Solution Means]A light measurement device 100 includes a phase adjustment unit 120 and a detector 140. The phase adjustment unit 120 outputs reference light E(R) based on object light E1 being light to be obtained by transmission or reflection of light E from a light source with respect to a measured object 200, and signal light E(S) whose phase is adjusted to be different from a phase of signal light. The detector 140 derives a transmission or reflection light intensity distribution or a refractive index of the measured object 200, based on interference light E2 between signal light E(S) and reference light E(R) to be output by the phase adjustment unit 120. An optical axis of light E from a light source is linearly disposed. The phase adjustment unit 120 and the detector 140 are disposed on the optical axis of light E from a light source.