A blood sugar condition is estimated by the steps of (1) measuring a urine sugar value A, (2) discriminating whether or not said measured urine sugar value A is less than a discriminating method classification boundary value, (3) when the measured urine sugar value A is less than the discriminating method classification boundary value, 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 said latest measured the urine sugar value A is measured, (4) calculating a difference between said averaged value X and said measured urine sugar value A, (5) when said difference {X - A} 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 said past predetermined period of time, (7) calculating a ratio between said measured urine sugar value A and said averaged value X, and, (8) when said ratio {A/X} is not greater than a first discriminating reference ratio, discriminating as being the blood sugar value decrease.
