An automatic blood pressure measuring instrument for measuring and displaying a blood pressure of a subject in a non-invasive manner includes a pressure sensor for obtaining a pulse wave signal from a wrist of the subject, a pulse wave signal processing section for amplifying, filtering, and removing noise from the pulse wave applied from the pressure sensor, electrocardiogram electrodes for obtaining an electrocardiogram signal of the subject, an electrocardiogram signal processing section for amplifying, filtering, and removing noise from the electrocardiogram signal, an A/D converting section for converting the pulse wave signal the electrocardiogram signal into digital signals, a controlling section for comparing and analyzing the digital pulse wave signal and the digital electrocardiogram signal to determine the blood pressure of the subject, and a display for displaying the blood pressure of the subject determined by the controlling section.