To provide a waveform determining apparatus and a waveform determination area setting method for heightening reliability to waveform determination by creating a highly accurate waveform determination area.

The waveform determination area E1 is set by a process for overwriting and displaying, on a display screen 20a of a display 20, waveforms W1-W5, captured as a plurality of conforming waveforms on the side of an apparatus main body; a process for simultaneously displaying, on the display screen 20a, both a maximum value line Lmax acquired by retrieving only dot lines which indicate maximum values from among the waveforms W1-W5 displayed on the display screen 20a and composing them as a dot row and a minimum value line Lmin acquired by retrieving only dot lines which indicate minimum values and composing them as a dot row; and a process for setting a band region of a prescribed width determined by the locational relation between the reference maximum value line Lmax and the reference minimum value line Lmin as the waveform determination area E1.