Disclosed is the tide level measuring method using the laser tide level measurement device and laser. And the accommodated penetration hole the wiring part in the optical section: photo receiver: center which is the condensed light as described above received it is prepared with the cone on the sleep it is wealthy it is mounted to the extended wiring part: wiring part leading end from the light-generating section to the inner portion of the tube well the scattered light is condensed the light-generating section: straight light in which the straight light is transmitted is transformed to the plane light is formed at this laser tide level measurement device According to the height of the surface of the water, the drifting buoy part, the reflecting body which is prepared in the upper side of the drifting buoy part and, the weight part, the phase detector detecting the transmitted light as described above and received optical phase difference as described above, and the transmitted light as described above and received optical phase difference as described above the error of measured tide level data by corrosion of the tidal observation apparatus using the drifting buoy part by the this, it calculates and data processing part, and the power supply unit which is provided with the external power supply and are included and the damage, the error of measurement data by the attractive force and error etc. are reduced. In that way it is the tidal observation circle the measurement cost can be cut down it can be exact and it make the reliability high tide level measurement possible. As to the data, the tide level is measured. As to the power supply unit which is provided with the external power supply and, the power source is supplied. The drifting buoy part the along the longitudinal direction is flown of the wiring part. As to the, the transmitted light as described above is reflected. As to the weight part, it is prepared in the leading end of the wiring part and it is locked in the underwater and in that way the flow of the wiring part is suppressed and the position of the reflecting body is fixed.