PURPOSE: To enhance operability, reliability and quickness by determining the extent of coloring of a test piece for measuring the components of urine through measurement of color tone using a three stimulus value measuring unit.

CONSTITUTION: A three stimulus value measuring unit calculates three stimulus values (X, Y, Z) of an object by means of a sensor (detector) having the sensitivity of isochromatic function corresponding to the spectral sensitivity of human eye. The light receiving system of the three stimulus value measuring unit comprises three optical detectors 7 for measuring the reflection light from a sample (test pieces 1, 2, 3 for measuring the urine components and a colored urine test piece 4), and three optical detectors 8 for monitoring the fluctuation of a light source 6. Output signals from the detectors 7, 8 are fed through a current/voltage conversion circuit 9 and an A/D conversion circuit 10 to a three stimulus value operating circuit 11 where the signals are converted into three stimulus values X, Y, Z. Furthermore, an operating circuit 12 compares the extent of coloring of the sample with the values on a preprogrammed qualitative decision table thus obtaining qualitative or quantitative results. The results are displayed 13 as the color tone information of colored urine, and the color and concentration information of sample urine.