1. A waveform recording apparatus for receiving an input drawing command and recording a waveform, based on said input drawing command, on paper having first and second ruled edge lines parallel one another at opposing first and second edges of said paper, wherein said first and second ruled edge lines define a paper coordinate system, the waveform recording apparatus comprising: a movable drawing head movable in a first direction according to said input drawing command; means for moving said paper in a second direction, perpendicular to said first direction, with said first and second ruled edge lines extending in said second direction, to permit said movable drawing head to draw over an area of said paper; a first ruled line offset detecting means and a second ruled line offset detecting means each for detecting a position of a ruled line; said first and second ruled line offset detecting means being respectively fixed at defined first and second positions respectively proximate said first and second edges of said paper to respectively permit detection of first and second offsets respectively of said first and second ruled edge lines from said first and second positions; ruled line spacing determination means for determining a line spacing distance between said first and second ruled edge lines in an apparatus coordinate system of said waveform recording apparatus based on said first and second offsets; coordinate system correspondence relationship means for determining a correspondence relationship between said paper coordinate system and said apparatus coordinate system based on a relation of said line spacing of said first and second ruled edge lines in said paper coordinate system with said line spacing in said apparatus coordinate and at least one of said first and second offsets; coordinate conversion means for converting said input drawing command which is in said paper coordinate system to a converted input drawing command in said apparatus coordinate system based on said correspondence relationship; and coordinate replacement means for replacing said input drawing command with said converted input drawing command during execution of said input drawing command.