The biological signal averaging processing device includes a waveform input unit (12) for continuously obtaining a biological signal in which analogous waves appear repeatedly, a summing-averaging processing unit (21) which sums the biological signal obtained from the waveform input unit each time a predetermined time period lapses after a desired start time point to obtain an average wave, a noise level detection part (22) which detects a noise level of random noise contained in the biological signal obtained from the waveform input unit each time the predetermined time period lapses after the desired start time point, a display part for displaying information, and a display control part (32) for displaying the information on the screen of the display part (31). The display control part displays the noise levels detected by the noise level detection part on the screen of the display part in a chronological manner in association with the respective predetermined time periods.
