There is provided a living body light measuring device capable of monitoring a time curve of a blood substance concentration as time curves of parameters of a signal waveform and judging or analyzing characteristic traits of a subject relevant to the parameters of the signal waveform, wherein a signal processor extracts parameters such as a peak value and latency from a hemoglobin signal waveform measured before and after substance intake of a testee, and generates and displays a time curve graph having a parameter and time respectively as its ordinate and abscissa. Influence of an intake substance upon blood component concentrations and blood flow can be monitored by monitoring the time curves of parameters of the signal waveform. A category processor classifies measurement data into categories, analyzes time curves of a plurality of parameters every category, and displays a result on a result viewer.