PROBLEM TO BE SOLVED: To make sure the operation of an underwater uncoupling device for heavy object.SOLUTION: When a heavy object 14 is suspended, a load applied to a release hook 62 is transmitted from the release hook 62 to a retaining ring 64 which is a load receiving part via plates 60a which are members configuring a load transfer system of a frame 60. Thus, an electric actuator 36, which opens and closes the release hook 62, itself does not receive the load applied to the release hook 62. Therefore, a load which an inventive underwater uncoupling device can receive can be determined according to the strength of the plates 60a, which are the members configuring the load transfer system of the frame 60, without being restricted by the endurance load of the electric actuator 36. Besides, a protector 68 covering the electric actuator 36 protects the electric actuator 36 from external pressure, thereby ensuring reliably opening and closing actuation of the release hook 62.
