PURPOSE: To facilitate the judgement of whether a blood sampling inspection is necessary or not by displaying an optical density difference correspondence value to be calculated from reflection factors of lights with first and second wavelengths and a serum bilirubin density correspondence value converted therefrom being switched from one to the other.

CONSTITUTION: When a probe is pressed on an object M to be inspected to turn ON a measuring switch 5a, light radiated from a xenon flash tube 18 impinges upon the object M to be inspected through a CPU 30 and a light emitting circuit 35 to be reflected in a subcutaneous tissue, divided with a dichroic mirror 13 and light of wavelengths thereof of nearly 450 and 550 nm impinges upon photodetectors 15 and 17 through optical BPFs 14 and 16. A part of the light from the tube 18 impinges upon a photodetector 20 for monitoring light. Detection signals of the elements 15, 17 and 20 are inputted into the CPU 30 through an A/D converter 36. The CPU 30 calculates an optical density difference correspondence value by a specified equation using the detection signals and a coefficient stored in a memory 39 and a serum bilirubin density correspondence value converted therefrom and the values are displayed on a display element 4 being switched by turning on or off a switch 3C at a function setting section 3.