A blood sugar condition is estimated by (1) measuring a urine sugar value A, (2) discriminating whether or not the measured urine sugar value is less than a discriminating method classification boundary value, (3) when it is less, obtaining an averaged value X of measured urine sugar values during a past predetermined period of time, measured at the same timing in a one-day life as the timing when the latest measured urine sugar value is measured, (4) calculating the difference between the averaged value and the measured urine sugar value, (5) when the difference is not less than a positive discriminating reference difference, discriminating as being a blood sugar value decrease, (6) when the measured urine sugar value A is not less than the discriminating method classification boundary value, obtaining an averaged value X of all measured urine sugar values during the past predetermined period of time, (7) calculating a ratio between the measured urine sugar value and the averaged value X, and, (8) when the ratio is not greater than a first discriminating reference ratio, discriminating as being the blood sugar value decrease.