To evaluate whether a bloodstream obtained by a measurement in normal or not directly after the measurement.

A blood velocity calculator 47a frequency-analyzes photodetecting signals of photomultipliers 46a and 46b, calculates a blood velocity, and outputs the velocity to a blood flow volume calculator 47d and a display unit 52. A blood vessel diameter calculator 47b calculates a blood vessel diameter from a blood vessel image imaged by a one-dimensional CCD 42, and outputs the diameter to the calculator 47d, a predicted blood stream referring unit 47c and the unit 52. The unit 47c reads a predicted bloodstream recorded in a flow data table recorder 51 based on a blood vessel diameter calculated by the calculator 4b and outputs the predicted volume to the unit 52. The calculator 47d calculates the blood flow volume from the velocity and the diameter, and outputs the volume to the unit 52. The measured volume is compared with the predicted bloodstream, and whether the volume is normal or not is evaluated.