PURPOSE: To quickly measure a flow direction as well as a flow velocity by specifying the depth of a water vein in a short time.

CONSTITUTION: The case of a measurement probe 10 traveling in a boring 5 is used as the first power supply electrode 14, and the second power supply electrode 15 is laid at a position off the boring 5. Also, an AC power source for supplying power across the first and second power supply electrodes 14 and 15, and a current indicator 25 for measuring supply current are provided on the ground. Before measuring the flow direction and velocity of water running in a vein with a picture tube device 21 for monitor, and a bearing indicator 22, the depth of the vein is specified on the basis of a change in supply current across the electrodes 14 and 15.