PURPOSE: To prevent the occurrence of difference in delivery pressure between an oil feeding nozzle of a main measuring instrument side and an oil feeding nozzle of an auxiliary measuring instrument side, and increase the working efficiency in oiling and also increase reliability thereof.

CONSTITUTION: A fixed orifice 11 as a pressure loss means is provided to increase the pressure loss P1 in the main oiling line due to a main measuring instrument 100 up to the pressure loss P2 in the auxiliary oiling line due to an auxiliary measuring instrument 20a, between an oil feeding hose 108 and a branch pipe 105 connected to an oil feeding nozzle 109 at the main measuring instrument 100 side. In this way, the hydraulic pressure and the flow speed delivered from the oil feeding nozzle 109 of the main measuring instrument 100 side and the oil feeding nozzle 204 of the auxiliary measuring instrument 200 side become substantially equal respectively.