PURPOSE: To easily operate waveform decision on the display screen of a display means and to reduce the load for the waveform decision by superimposing a waveform to be measured on a reference range set and displayed on the display screen.

CONSTITUTION: An arithmetic control part 21 is equipped with a plotting process instruction executing means 22, a cursor display means 23, and a cursor moving means 24. An operation part 11 instructs this arithmetic control part 21 to perform necessary processes and the output of the arithmetic control part 21 is displayed on the display screen 32 of the display means 31. Then the plotting process instruction executing means 22 of the arithmetic control part 21 performs necessary plotting processes on the display screen 32, a cursor moving means 24 moves a cursor on the display screen 32, and a cursor display means 23 moves and display the cursor on the display screen 32 at other specified points, thereby performing plotting and editing operation for deciding the waveform on the display screen 32.