In order to easily understand a synthetic quality degree, a ratio of each of parameters in the entirety, etc. in an ATM line (10) to be evaluated, cell data is received from the ATM line and abnormal cells are detected by a misinserted cell detection section (21), a lost cell detection section (23) and an errored cell detection section (25). The numbers of abnormal cells occurring in the same time period are counted by a misinserted cell count section (22), a lost cell count section (24) and an errored cell count section (26). A total number graph display section (27) displays a strip-shaped total number graph, which corresponds in length to a sum of count results of the respective count sections (22, 24, 26), successively on a time-axis of a screen of a display device (32). An items display section (28) discriminatively displays a plurality of regions into which the total number graph is divided such that the regions have lengths corresponding to the numbers of abnormal cells counted by the respective count sections (22, 24, 26).