PURPOSE: To enable a flow rate of an optional angle to be measured with high accuracy even in case that a flow rate of fluid is small or that a fluid flows in rectangular direction to a supersonic beam by finding out a flow rate of moving matter in a subject's body from a space distribution shift of echo and a time lag.

CONSTITUTION: One scanning cycle of a supersonic flow rate measurement apparatus consists of a data uptake process and an operation process. In the data uptake process, a supersonic echo signal received by a probe 100 is sampled at a specified time and stored in a data memory 108, and in the operation process, a quantity of space distribution shift of echo is detected from the stored echo strength information of two scannings. In an operation for finding out a flow rate, a CPU 106 reads out the space distribution of echo strength information stored in the data memory 108 according to a flow rate detection processing routine stored in a program memory 109, processes and finds out that rate. It is made possible to measure a flow rate of an optional angle with high accuracy by this apparatus.