PURPOSE: To obtain the compact system that can be operated readily by connecting a control mechanism to a detector and an agitator through a control block.

CONSTITUTION: This is a liquid/liquid interface, e.g. a mercury/solution interface. An internal storage device 29 is connected to an independent storage device 114. Thus, a control mechanism 25 is connected via a control block 115 as necessary to a detector 116, which detects the shape of the water droplets or the shape of bubbles immersed in liquid to be measured 117 together with a thin pipe 21, and an agitator 54. Furthermore, a control block 115 is connected to the storage device 114 and connected to a detection evaluating block 118, which records and evaluates the inspection results. This device becomes the electrode/sensor including the very small drops and bubbles or the electrode sensor. The flow passing the thin pipe 21 is controlled by the electrically controlled value. Therefore, the growing time of the drop, i.e., the drop size can be selected.