Abstract: A method for detecting death process of a cell or tissue of a living subject. In one embodiment, the method includes the steps of illuminating the cell or tissue of the living subject with a coherent light, collecting fluorescent light returned from the illuminated cell or tissue of the living subject, identifying a NAD(P)H peak of a spectrum of the collected fluorescent light with a wavelength, ?peak, and obtaining the intensity of the NAD(P)H peak of the spectrum of the collected fluorescent light substantially corresponding to the wavelength ?peak. These steps are repeated at sequential stages until the intensity of the NAD(P)H peak of the spectrum at a current stage is less than the intensity of the NAD(P)H peak of the spectrum at an earlier stage immediately prior to the current stage so as to detect death process of the cell of the living subject at the current stage using the intensity of the NAD(P)H peak of the spectrum.