PURPOSE: To improve the maneuverability of a tower and to improve the workability, by making a tower supported by a plurality of floats at the outercircumference shrinkable/expandable through the operation of a winch and enabling the towing under the shrinked state while enabling the anchoring at the predetermined sea region under the expanded state.

CONSTITUTION: A plurality of tubular members are coupled telescopically to construct a shrinkable/expandable tower, then the outercircumference of said tower is surrounded by a plurality of floats 1 coupled each other to support said tower in the ocean. A bottom base tower A1 at the lowermost of the tower and a winch B6 arranged on said float 1 are coupled through a wire B5, and when winding or rewinding the winch B6 said tower A1 will move up and down to shrink/expand the tower. With such structure the tower is shrinked when towing while expanded to reach to the sea bottom when anchoring the tower at the predetermined sea region and the float is removed as required.