This authentication device is equipped with: an acquisition unit for acquiring measurement data which includes a measured value and measurement time information associated with the measured value from a biometric information measurement device for measuring a biometric information value; a provision unit for providing a function which should be used by one specific user; a sensor unit which includes at least one sensor; an estimation unit for estimating the state of the specific user during the time range specified by the measurement time information, on the basis of the information acquired by the sensor unit; and an identification unit for identifying whether the measured value pertains to the specific user or not, on the basis of the state estimation results and whether or not the function was usable during the time range.