An ultrasonic blood pressure measuring device receives a reflected wave of an ultrasonic wave transmitted to a blood vessel, and measures the degree of displacement of a blood vessel wall of the blood vessel based on the reflected wave of the ultrasonic wave during at least one heartbeat period. Then, cardiac systolic blood pressure and cardiac diastolic blood pressure are calculated from a maximum value of the blood vessel diameter, which appears after the peak of the degree of displacement of the blood vessel wall, and a minimum value of the blood vessel diameter, which appears before the peak, using a correlation between the diameter of blood vessel and blood pressure set in advance.
