A device for measuring optical properties is provided which is equipped with an exciting light source for emitting exciting light to the sites to be measured of a sample, a light intensity modulator for modulating the exciting light, a probe light source for emitting probe light and a detector for receiving the probe light. The device is characterized by comprising an intensity distribution modifying means for bringing the maximum intensity portion of said probe light close to the sample when the probe light emitted from the probe light source reaches the site to be measured or the vicinity thereof. A method for measuring optical properties using the device is also provided. This device is useful particularly for measurement of the light absorption characteristics of a monomolecular film spread on a liquid surface.