PURPOSE: To enable the image display of the living body signal which can intuitively be grasped by finding two-dimensional coordinates for drawing amplitude values of living body signal data corresponding to the radii of circles, and writing the two-dimensional coordinate positions in specific locations of a bit map memory corresponding to respective display dots on a display screen.

CONSTITUTION: A CPU 3 clears the storage contents of the bit map memory 7 to an initial state, places 0 at a starting point on a set circumference, and inputs the living body signal data from an A-D converter 1. The CPU 3 finds the angle of the amplitude of the living body signal data at the point 0, calculates the two-dimensional coordinates corresponding to the amplitude of the angle, and transfers the two-dimensional coordinate data to the bit map memory 7, thereby writing the data as an image at the positions corresponding to the respective display dots on the screen of a display device 8. Then the two-dimensional coordinate data are read out of the bit map memory 7 and sent out to the display device 8, which displays them on its screen.