PURPOSE: To efficiently increase the flowing velocity of tide and obtain a high output by a relatively small water wheel, by providing multistage flow converging pipes, each of which has a major-diameter inlet port and a minor-diameter outlet port.

CONSTITUTION: A float 1 is anchored so that the axis of the flow converging pipes 2, 3 almost coincides with the direction of the tide. The seawater is guided on the oblique face of the front bottom of the float 1 so that the seawater is conducted into the first-stage flow converging pipe 2. Because the diameter of the outlet port of the pipe 2 is smaller than that of its inlet port, the flowing velocity of the seawater is increased and its pressure is decreased according to Bernoulli's theorem. A large amount of seawater is thus brought to the second-stage flow converging pipe 3. The flowing velocity of the seat seawater is increased further by the pipe 3 to rotate the water wheel installed in the pipe 3 to produce electric power by a dynamo 5.