To provide a data display method capable of effectively displaying a summary even if aimed at a large number of time-series data.

This method is provided with a step for inputting time-series data, step for extracting a trend component and a mean value by statistically processing these time-series data, step for displaying the mean value of the time-series data on each of time-series data collection units on a display picture for displaying a time-series data collection unit name on X axis and displaying the value of the time-series data on Y axis, and step for displaying the value of the trend component of each of time-series data collection units at a position including the mean value with a mark having a length, a size, a form and a color corresponding to the level of that value. The mark for displaying the value of the trend component can be made into arrow with the mean value as a starting end point. Further, concerning each of time-series data collection units, a target value or allowable limit value can be displayed while being superimposed on the display picture as well.