To provide a waveform observing apparatus suppressed in the influence of the heat of terminal blocks.

The waveform observing apparatus includes measuring units 23 composed of terminal blocks 25 for receiving wiring conductors from measuring instruments and measuring modules 230 for converting measurement data received from the measuring instruments through the terminal blocks 25 into digital signals, and stores the measurement data received from the measuring units 23 on a memory 30 and performs the waveform display of the data on a display 224. The waveform observing apparatus has: at least one pair of vertical walls 210, 212 provided at right and left sides of its body case 205 separately; a module insertion space S which is constituted of the mutually-opposed wall surfaces of the one pair of vertical walls 210, 212, and receives a plurality of measuring modules 230 in a state that they are arranged in a line vertically; and vertically-penetrating ventilating apertures 58 formed in the upper and lower cases 50, 52 divided and separatable into upper and lower portions of the measuring units 23 at portions adjoining the terminal blocks 25 of the upper and lower cases 50, 52.