A detection-rate calculating unit calculates a detection rate representing a ratio of number of interval data representing a time interval of one cycle of a waveform of at least one of a pulse and a heart rate, generated within a predetermined reference time to a sum of the number of the interval data and number of error data representing a content of an error occurred while the interval data is generated. When the detection rate is larger than the first threshold, an index calculating unit calculates an autonomic-nervous index representing an autonomic-nervous activity state, based on the interval data generated within the reference time.
