A practical measuring device and a measuring method that allow simply measuring average postprandial blood glucose from urinary glucose. The blood glucose measuring device includes a measuring unit that measures postprandial urinary glucose from subjects urine at a predetermined time after meal, a processing unit that calculates average postprandial blood glucose through a period up to the predetermined time after meal, based on the postprandial urinary glucose, a storage unit that stores calibration data including the postprandial urinary glucose and the average postprandial blood glucose in association, and an output unit that outputs data indicating the calculated average postprandial blood glucose. The processing unit calculates the average postprandial blood glucose, based on the postprandial urinary glucose from the urine of the subject who has intaken a desired amount of water or perspired in the period up to the predetermined time after meal, and the calibration data.
