There is provided a waveform observing apparatus with a reduced depth in such a manner that the waveform observing apparatus is one including a terminal board, connecting wiring extending from external equipment, a memory for receiving measured data through the terminal board, to store the measured data, and a display for displaying the measured data in waveform, the apparatus including: a first intra-body substrate, installed in an erect state inside a body frame of the waveform observing apparatus; a plurality of first connectors, provided on the first intra-body substrate; and a measurement module, which is connector-connected to the first connector of the first intra-body substrate, to be installed between the first intra-body substrate and the terminal board, and also includes a measurement circuit, wherein a plurality of measurement modules are detachable in an aligned state with respect to the erect first intra-body substrate.