PURPOSE: To maintain the minimum oil pressure at the time of automatic starting at a high level by starting an emergency oil pump, when the oil pressure has lowered violently, early through the action of an oil pressure drop speed sensor.

CONSTITUTION: Each of the lines for control oils 3a, 3b, 3c, a bearing oil 6 and a suction supply oil 10 is equipped with a pressure switch 13aW13d and a pressure drop speed sensor 14aW14d. When the speed of drop of the line oil pressure has exceeded a certain specified value, the pressure drop speed sensors 14aW14d will sense it to actuate starting of a backup motor-operated oil pump. Accordingly if the line oil pressure drops violently, this backup pump will start to commence oil supply. Thereby the minimum oil pressure point 29 will become higher than the one 25, and thus the reliability for operation and maintenance of the steam turbine is enhanced.