a body movement determining unit configured to determine that the body movement occurs if a fluctuation amount of the body movement data is greater than a first predetermined threshold;

a pulse interval data processor that processes the series of pulse interval data, after removing pulse interval data measured in parallel with the body movement data from the series of pulse interval data, if the body movement determining unit determines that the body movement occurs, and thereafter processes the series of pulse interval data other than the removed pulse interval data;

a sleep state determining unit configured to determine the sleep state based on autonomic nerve indexes acquired from the series of pulse interval data processed by the pulse interval data processor;

an awakening determining unit configured to determine that the body movement occurs during awakening if an occurrence frequency of the body movement determined by the body movement determining unit is equal to or greater than a second predetermined threshold, and to determine that the body movement occurs during sleep if the occurrence frequency of the body movement is smaller than the second predetermined threshold, wherein the pulse interval data processor that processes the series of pulse interval data after removing the pulse interval data measured in parallel with the body movement data, determined as the body movement during sleep from the series of pulse interval data, if the awakening determining unit determines that the body movement occurs during sleep;

an abnormality data remover that removes the pulse interval data measured in parallel with the body movement data determined as the body movement by the awakening determining unit from the series of pulse interval data, if the awakening determining unit determines that the body movement occurs, and the pulse interval data processor that processes the series of pulse interval data after the abnormality data remover removes the pulse interval data measured in parallel with the body movement data determined as the body movement from the series of pulse interval data;

a pulse interval data interpolating unit configured to interpolate the series of pulse interval data, from which the abnormality data remover removes the pulse interval data measured in parallel with the body movement data determined as the body movement, wherein the pulse interval data processor processes the series of pulse interval data temporally equidistant based on the series of pulse interval data interpolated by the pulse interval data interpolating unit;

a body movement measuring unit configured to measure acceleration data in three-axis directions as the body movement data; and

a body movement sampling data processor that differentiates the acceleration data in the three-axis directions measured by the body movement measuring unit by time, that obtains differential coefficients of the acceleration data in the three-axis directions, and that calculates a fluctuation amount of the body movement data, the fluctuation amount of the body movement data being a square root of a sum of squares of the differential coefficients of the acceleration data in the three-axis directions, wherein the body movement determining unit is configured to determine that the body movement occurs if the fluctuation amount of the body movement data calculated by the body movement sampling data processor is greater than the first predetermined threshold.