A degassing device capable of regulating an amount of air dissolved in a liquid. A device for measuring amounts of dissolved oxygen measures the amount of oxygen dissolved in one of a coating liquid which has yet to be degassed, and is to be fed to a film degassing device, and a coating liquid which has been degassed and discharged from the film degassing device. Based on measured results, a control unit regulates the degree of opening of a vacuum valve so as to change the degree of degassing performed by the film degassing device, thereby suppressing fluctuations in an amount of oxygen dissolved in the coating liquid. A load never constantly acts on the film all the time, the film life can accordingly be extended, thus resulting in reductions in running costs.