To provide an offshore structure capable of effectively reducing rolling caused by waves and wind with a simple device.

An upper structure 4 is installed on a floating body 3 through a supporting control device 7 and an attitude control device 8 operated by a signal from a controller 18. The supporting control device 7 comprises a plurality of supporting devices 9 formed by installing hydraulic cylinders 12 on a quake isolator 11 and a hydraulic control device 10 for controlling the telescoping of the hydraulic cylinders 12. The attitude control device 8 comprises an actuator 16 for vertical control and an actuator 17 for horizontal control. A motion detecting sensor 19 installed on the floating body 3 is connected electrically to the controller 18.