PURPOSE: To obtain a device which continuously and precisely measures or controls the height difference between a plurality of spots or the change of the height difference.

CONSTITUTION: A device for measuring or controlling height difference is provided with closed pots 2 which are respectively installed to different spots and the pots 2 are partially filled with a liquid 53 and form a liquid circuit 31 when the pots 2 are coupled with a liquid conduit connected to the bottom sections of the pots 2. The pots 2 also form a gas circuit 36 when the pots 2 are coupled with a gas conduit connected to the top sections of the pots 2. Each pot is provided with a proximity capacity pickup 11 and the pickup 11 has at least two electrodes which are separated from each other in the horizontal direction. Each pickup 11 is positioned in the corresponding pot, with the bottom face being maintained above the upper surface 54 of the liquid in the pot at a distance, and generates a signal indicating the vertical position of the upper surface of the liquid and the device is also provided with devices 56 and 57 which compare the signals generated from the pickups 11 with each other. Therefore, the information on the positional relation among the pots, accordingly, the spots or the vertical positions of the spots from a certain reference vertical position can be obtained.