PURPOSE: To achieve an image visible easily by increasing an apparent frame rate even in a blood stream image slow in the frame rate in an ultrasonic Doppler blood stream measuring apparatus which performs a two-dimensional display of blood stream information.

CONSTITUTION: A plurality of image memories 7a-7c provided at a memory means 7 are switched in a specified sequence with an input switch 10 and an output switch 11 to change over the writing of data into and the reading thereof out of the respective image memories 7a-7c, and a correlation processing is performed between the data read out of the image memories 7a-7c with a correlation processor 12, which is controlled with a control circuit 13. This enables the generation of image data corresponding to a plurality of images within image construction time per frame of a TV monitor 9, thereby achieving a higher apparent frame rate.