Abstract: A level marking apparatus capable of directly measuring height comprises an elastic synthetic resin tube. One end of the tube is secured to a pressure sensor capable of producing an output voltage and air-tightly sealed, and the other end of the tube is connected to a reference instrument, which has a larger diameter and is shorter in length than the tube. The tube is totally filled with low viscosity macromolecule liquid. Moreover, the pressure sensor is connected to a micro computer programmed to find an average value of fluctuation waveform within a certain cycle of output voltage of the pressure sensor. The micro computer also calculates and memorizes a reference level based on a pressure difference between the reference instrument and the pressure sensor when placed at different heights. Additionally, a marking device is connected to the pressure sensor, and it is actuated by an ON signal from the pressure sensor.