To provide a structure capable of floating/sinking in water with its upper part usable for various purposes.

The sinkable type foundation structure 1 is composed of foamed polystyrene attached with polyurea, a weight 5, a float, etc. The sinkable type foundation structure 1 can float/sink to a demanded water level by adding/removing sand to/from the weight 5, also can be in a horizontal state by correcting the inclination state, and can be in a demanded inclination state by inclining the horizontal state. The sinkable foundation structure 1 is used for a field, gardening on the water, a farm, a biotope, etc. Hydroponics by floating the structure absorbs nitrogen, phosphor, potash, etc., from water of a pond and improves the quality of the water.