At wastewater treatment facilities of various types of manufacturing plants, pollution load monitoring (upstream monitoring) is becoming increasingly important to ensure appropriate and stable operation and water pollution accident prevention. Pollution load varies depending on the operating status of the plant, so continuous monitoring is essential. Continuous and stable measurement of TOC in high-pollution samples such as the influent water in wastewater treatment facilities is not easy. In particular, paper mill wastewater, in addition to containing large amounts of pulp residue, provides an environment that facilitates microorganism proliferation. Here, using the online TOC-4200, we introduce an example of continuous measurement of paper mill wastewater having such characteristics.