A biometric information processing device has a heart rate detection unit that detects the heart rate of a subject a relative heart rate calculation unit that calculates a relative heart rate, which is the relative value of the heart rate to the prescribed resting heart rate of the subject a relative oxygen intake calculation unit that calculates a relative oxygen intake based on the relative heart rate an oxygen intake estimation unit that estimates the oxygen intake from the relative oxygen intake and a calorie expenditure calculation unit that calculates calorie expenditure based on the oxygen intake.