PURPOSE: To obtain a stable liquid feeding amount by controlling the pressure at the inflow side within a pressure range corresponding to the stable range of transported amount, by obtaining a necessary pressure through upper arrangement of transportation source and utilization of water head or by using pressurizing means such as compressor.

CONSTITUTION: In order to obtain a stable liquid feeding amount, liquid supplying bottles 20 are arranged at a position sufficiently higher than two-series roller pump 12 so that the pressure at the inflow side of the two-series roller pump 12 becomes sufficiently high, or the air which passes through a filter 18 is injected under pressure into the liquid supplying bottles 20 by the use of a compressor 17, and thus the pressure at the pump inflow side is increased. In order to prevent the breakage of the liquid feeding line 7 due to excess pressure, a pressure sensor 19 is positioned at the inflow side of the two-series roller pump 12 in the liquid feeding line 7, and the opening degree of the leak valve 15 arranged between the compressor 17 and the liquid feeding bottles 20 is controlled, and thus excess pressure can be avoided.