The present invention addresses the problem of providing a novel technique for producing aqueous chlorous acid. The present invention provides a method for producing chlorous acid, which comprises a step of adding chlorine dioxide (ClO2) to one or more components independently selected from an inorganic acid, an inorganic acid salt, an organic acid and an organic acid salt or a combination of two or more of the aforementioned components. In the method, chlorine dioxide (ClO2) is provided in the form of a gas. The method also comprises, subsequent to the above-mentioned addition step, a step of further adding one or more components independently selected from an inorganic acid, an inorganic acid salt, an organic acid and an organic acid salt or a combination of two or more of the aforementioned components.
