To accurately detect the residual amount of stock solution inexpensively rather than the conventional case.

A detection coil 11 of sensor part 1 is fitted to a tube 17 for stock solution extraction, and a high frequency signal is transmitted from an oscillation part 2 through a transmission line 4 to the sensor part 1. Since the sensor part 1 can be matched with the transmission line 4 and no reflected signal is returned when there is no stock solution in the tube 17 for stock solution extraction, the level of signal outputted from a detection part 3 is low and a signal converter 5 outputs a signal showing the absence of stock solution. Oppositely when there is a stock solution in the tube 17 for stock solution extraction, the level of reflected signal from the sensor part 1 is high and the signal converter 5 outputs a signal showing the presence of stock solution. A display 6 receives this signal showing the absence or presence of stock solution and displays it.