An information processing system comprising: a normal value learning database keeping learning data continuously acquired from a monitoring target, wherein said learning data consists of the monitoring data determined as having a normal value for the monitoring target; a setting unit adapted to form a band model by setting a normal range of the learning data received from the normal value learning database, wherein the setting unit is adapted to compute a mean of the learning data and further adapted to compute an upper limit (306, M U (t)) and a lower limit (307, M L (t)) for the normal range; a determination unit adapted to determine whether the time series data collected from sensors of the monitoring target are out of the normal range of the band model set by the setting unit, and if the time series data are out of the normal range, to output a determined time (t2, 502) corresponding to the time the time series data went out of the normal range; and a detection unit adapted to receive the determined time (t2, 502) from the determination unit and adapted to determine a start time (t3, 601) that is before the determined time (t2, 502) and that corresponds to the time when the time series data start to show an anomaly that is detected by the detection unit when the inclination value of the degree of deviation curve reaches or exceeds a first threshold, wherein the deviation represents the deviation of the time series data from the mean of the learning data as computed by the setting unit; and a display unit adapted to display the time series data with the determined time (t2, 502) and the start time (t3, 601). a normal value learning database keeping learning data continuously acquired from a monitoring target, wherein said learning data consists of the monitoring data determined as having a normal value for the monitoring target; a setting unit adapted to form a band model by setting a normal range of the learning data received from the normal value learning database, wherein the setting unit is adapted to compute a mean of the learning data and further adapted to compute an upper limit (306, M U (t)) and a lower limit (307, M L (t)) for the normal range; a determination unit adapted to determine whether the time series data collected from sensors of the monitoring target are out of the normal range of the band model set by the setting unit, and if the time series data are out of the normal range, to output a determined time (t2, 502) corresponding to the time the time series data went out of the normal range; and a detection unit adapted to receive the determined time (t2, 502) from the determination unit and adapted to determine a start time (t3, 601) that is before the determined time (t2, 502) and that corresponds to the time when the time series data start to show an anomaly that is detected by the detection unit when the inclination value of the degree of deviation curve reaches or exceeds a first threshold, wherein the deviation represents the deviation of the time series data from the mean of the learning data as computed by the setting unit; and a display unit adapted to display the time series data with the determined time (t2, 502) and the start time (t3, 601).