To provide a floating type foundation structure allowing a generator system to be installed, even far out at sea irrespective of the marine ground shape at all, in which the water depth hardly exerts no affection.

The float type foundation structure 1 is for supporting the generator system 2 upright on the ocean and is configured so that the upright supporting part of the generator system 2 is installed concentrically directly under the generator system 2; and a main float 5 is installed in a position deep under the static water surface; and a mooring device 7 is provided at the end of the main float 5, while a swing preventive member 8 is installed beside of the main float 5. Thereby it is possible to suppress swings of the whole device as much as possible, which results due to the influence of the external force of waves, winds, etc., even far out on the ocean having tendency of increasing marine wind speed, irrespective of the marine ground shape being hardly influenced by the water depth. This also adds fish bank effects of fishes, etc., to its lower part.