A biological photometer having, in its signal processing unit, a memory unit in which characteristics of hemoglobin change pattern of healthy case and various diseases are stored as reference template, characteristic extraction unit in which characteristic of hemoglobin change patterns are extracted from hemoglobin signals measured in a photometer unit, and a judgment unit in which the characteristics of the hemoglobin change patterns thus extracted are compared with the reference templates stored in the memory unit so as to judge whether the subject is healthy or ill. As the characteristics of the hemoglobin change pattern, use is made of hemoglobin change pattern curve as well as factors determined therefrom such as latent time, maximum level, time for attaining the maximum level, differential quantitative change, integral quantitative change, etc. Using this biological photometer, various diseases can be easily and quantitatively diagnosed.