To provide an optical measuring instrument capable of more efficient transmitted illumination of a specimen, without large sizing of the whole instrument.

In this optical measuring instrument, a transmitted illumination panel 35 composed of a plurality of light-emitting diodes arranged in parallel is disposed on a stage 31 on which a specimen 12 is to be placed. When the size of the specimen 12 is measured, a controller 22 calculates the center location of the observation field of an object lens 32 on the stage 31 according to a moving amount of the stage 31. Then the controller 22, on the basis of the calculated center location and the size of the observation field of the object lens 32, controls lighting of each light-emitting diode so that only the light-emitting diodes forming the transmitted illumination panel 35 which are within the observation field of the object lens 32 emit light. This invention is applicable to the optical measuring instrument.