PURPOSE: To reduce information lost due to compression as much as possible when a waveform is compressed and displayed.

CONSTITUTION: This device is provided with a display device 80 whose display resolution in the direction of waveform transition is (m) dot and a waveform memory 50 capable of storing waveform data by (n) (n>m) samples, and when the number of waveform samples within the range required to be displayed among storage data in the waveform memory 50 is set to be (k) (n≥k>m), the waveform is compressed and displayed every samples of k/m pieces of the waveform sample within the range required to be displayed corresponding to the display value of each dot position on the display device 80 in the direction of waveform transition. This device is provided with a compression means 60 calculating frequency distribution in waveform data at every samples of k/m pieces of the waveform sample within the range required to be displayed. The frequency distribution calculated by the compression means 60 is displayed corresponding to luminance information in display data after compressed.