A blood pressure measuring device includes: a blood vessel diameter measurement unit which measures a blood vessel diameter of a measurement target blood vessel of a subject a pressurizing-type sphygmomanometer which acquires a blood pressure of the subject a calculation unit which calculates a correlation between the blood vessel diameter and the blood pressure on the basis of a result of the measurement by the blood vessel diameter measurement unit and a result of the measurement by the pressurizing-type sphygmomanometer at plural timings during artificial dialysis on the subject with different blood pressure values and a blood pressure calculation unit which calculates a blood pressure on the basis of the blood vessel diameter of the blood vessel measured by the blood vessel diameter measurement unit, using the correlation, after the artificial dialysis.
