This living-body light measuring device is characterized in including: one or a plurality of light source units each of which irradiate a subject with light modulated using a prescribed modulation frequency； one or a plurality of light detecting units each of which detect an optical signal based on the light radiated from the one or plurality of light sources； a signal acquiring unit which multiplies the optical signal detected by each of the one or plurality of light detecting units by a signal having the prescribed modulation frequency corresponding to the respective light source unit, and which acquires the resulting signal as a signal radiated from the respective light source unit； an analog-digital converter which subjects each signal acquired by the signal acquiring unit to analog-digital conversion using a prescribed sampling frequency； and a computing unit which integrates the signals converted by the analog-digital converter. This living-body light measuring device is also characterized in that the sampling frequency is an even multiple of all the modulation frequencies, and the time over which the computing unit performs the integration is an integral multiple of all the modulated signal periods, being the reciprocal of all the modulation frequencies.
