PURPOSE: To prevent the occurrence of an accident caused by the judgement errors and instruction input errors of an operator by storing conditions having the possibility of causing accident beforehand and preventing the opening/closing of a valve having the possibility of causing accident from being immediately performed.

CONSTITUTION: In the open state of the valve to be opened at the time of recovering oil in an oil recovery tank RTK-2, when the valve to be opened at the time of reception is opened, the oil is made to backflow from the oil recovery tank in a direction on the sea and the danger of oil leakage on the sea is generated. The open state of the valve with such danger is stored as a care needing valve open state combination list beforehand and an alarm is issued when a valve opening instruction which comes under the list is generated. Also, when the valves of FOD-1, 2, 3 and 4 and an FD-801-2 are turned to a closed state after heavy oil and crude oil are recovered through the FOD-1 in the oil recovery tank RTK-2, confinement of the oil inside piping is performed. When such a state is generated, the possibility of damaging the piping is predicted and the alarm of that effect is issued.