PURPOSE: To do away with an accumulator and prevent lowering of control pressure at a minimum by making an emergency oil pump automatically startable even when all main shaft pumps are stopped under the condition of automatic operating switch on.

CONSTITUTION: Under the condition of an automatic operating switch on, while a main oil pump 2 is not operating and when a main oil pump 1 stops, unillustrated first and second detector signals generate simultaneously to start a main oil pump 2 via circuit and cover a flow Q20 by a high pressure system and at the same time start an emergency oil pump 3 at a low pressure system supplementing a flow QE at the downstream of a bearing oil pressure regulating valve 6. By this way, bearing oil pressure is raised and accordingly the bearing oil pressure regulating valve 6 functions to reduce the flow which passes here and cover a control unit oil volume Q22 and lowering of control oil pressure can be prevented at a minimum without requiring an accumulator.