A noninvasive blood sugar level measurement method includes a process of changing a blood sugar level of a biological body, a process of noninvasively measuring biological feature amounts at plural measurement points that are timewise shifted from each other, a process of invasively measuring blood sugar levels of the biological body by the number of times that is lesser than the measurement points of the biological feature amount, a process of obtaining an approximate curve indicating temporal change in the actually measured blood sugar level that is obtained by the invasive measurement, a process of obtaining, using the obtained approximate curve, blood sugar levels (interpolation blood sugar levels) that would be obtained by the invasive measurement at the measurement times when the biological feature amounts are noninvasively measured, and a process of associating the values of the biological feature amounts at the times corresponding to the respective measurement points of the biological feature amounts with the interpolation blood sugar levels at the respective times, thereby forming a correlation table having plural sets of the biological feature amounts and the interpolation blood sugar levels. Therefore, even when the change in the biological feature amount relative to the blood sugar level is not monotonous, it is possible to form a precise correlation table without increasing the number of times of the invasive blood sugar level measurement.