The invention relates to a biometric information detecting apparatus for monitoring a state of a living body based on information constituted by adding an auxiliary data capable of determining a measuring state when biometric information is measured to a biometric state value. A biometric information detecting apparatus of the invention includes a biometric sensor for measuring biometric information for a predetermined time period, A/D conversion means for acquiring a sampling data by subjecting an output of the biometric sensor to A/D conversion, storing means for storing the sampling data, frequency analyzing means for subjecting the sampling data stored to the storing means to a frequency analysis and storing a result of the analysis to the storing portion, biometric state value calculating means for calculating a biometric state value from the result of the frequency analysis stored to the storing means, SN ratio calculating means for calculating an SN ratio from the result of the frequency analysis stored to the storing means, determining means for determining a reliability of the biometric state value based on whether the SN ratio exceeds a predetermined threshold, and measured data preserving means for correlating to store a result of determining the reliability and the biometric state value.