A method of cufflessly and non-invasively measuring blood pressure in a wrist region of a patient in association with a communication device that relays the information being measured includes: detecting a magnitude difference between a plurality of pulse wave signals detected from a wrist of a user; detecting feature points from an electrocardiogram (ECG) and pulse wave signals detected from the user; extracting variables needed to calculate the highest blood pressure and the lowest blood pressure using the detected feature points; and calculating the highest blood pressure and the lowest blood pressure of the user by deducing a scatter diagram using the extracted variables.