The microphotometer records the transmission in the primary image of an object down to 2-3 μ² under visual control. The electrical construction gives a linear amplification in the transmission range actually used. The object is moved across the measuring light beam and, synchronously, the transmission curve is recorded by the writer. The accuracy of the apparatus was found to be less than 1%. When the test included the photographic-photometric procedure in X-ray microradiography the standard error was ±1.5%.