PURPOSE: To always manage a residue of oxygen accurately without giving a patient any burden by arranging a data input means to input a data of applying condition through a modem from a telephone circuit.

CONSTITUTION: A display control circuit measures a liquid level with a measuring element 6, and LEDs 11 at a display section 7 are lit according to the liquid level. As each decrease occurs in a residue data sequentially, an output control circuit 15 calls up a master station B through a telephone circuit L to output the residue data after the decrease thereof and a slave station identification data. On the other hand, a personal computer 21 of the master station B inputs the residue data after the decrease thereof and slave station identification data through the telephone circuit L from the output control circuit 15 of each slave station A. Each time inputted, the residue data and the slave station identification data are displayed on a CRT22. This allows a monitoring person of the master station B to determine a liquid residue of each slave station A based on the data displayed. For example, when the residue decreases by 1/4, the replacement of a new reservoir 2 or the like is possible to handle.