Abstract: An electrocardiogram signal processing apparatus includes an analog-to-digital converter, and first, second and third processors. The analog-to-digital converter converts the input electrocardiogram signal into a digital signal. The first processor processes the digital signal by secondary differentiation to produce a secondary differentiated signal. The second processor detects the onset of the QRS complex in accordance with an input signal from the first processor, and the third processor recognizes a delta wave which is peculiar to an electrocardiogram of the Wolff-Parkinson-White syndrome in accordance with the digital signal, the secondary differentiated signal and the onset location of the QRS complex.