An apparatus to measure the pollution level of the surface of a photovoltaic module. A resistance change on the surface of a photovoltaic module is sensed to effectively measure the pollution level on the surface of the photovoltaic module and secure a proper cleaning cycle of the module during solar light power generation. The apparatus includes a glass substrate attachably mounted on the surface of a photovoltaic module. A reactive coating layer is coated on one side of the glass substrate, has a structure that pollutants are accumulated on one side surface, and causes a resistance change by contact with the pollutants. A signal processor connected to the reactive coating layer to receive a signal of the resistance change, operationally process the signal to measure a change in the resistance value caused by accumulation of the pollutants, and output a discrimination signal on pollution.