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