In an ultrasonic measuring apparatus, an addition/averaging-period setting unit determines a blood vessel diameter stable period in which a blood vessel diameter is in a stable state in one heartbeat period and sets the blood vessel diameter stable period as an addition and averaging period. An adding and averaging unit adds up and averages reflected wave measurement data measured in the addition and averaging period set by the addition/averaging-period setting unit. A blood-vessel-diameter calculating unit calculates a blood vessel inner diameter of a blood vessel using combined data obtained by the addition and averaging of the adding and averaging unit.
