An electrocardiographic waveform measuring apparatus mounted in a seat with a seat skin element includes: a sensor electrode at a seat interior side of the seat to be covered with the seat skin element an insulating elastic element at the seat interior side of the sensor electrode in the seat opposite to the seat skin element to face the sensor electrode a guard electrode at the seat interior side of the insulating elastic element in the seat opposite to the sensor electrode to be opposed to the sensor electrode through the insulating elastic element and a housing case at the seat interior side of the insulating elastic element in the seat opposite to the sensor electrode to be opposite to the insulating elastic element. The housing case accommodates a sensor circuit with an amplifier circuit, to which a potential signal of the sensor electrode is initially input.
