A method for producing halogen oxyacid, which includes a step of continuously supplying and mixing an organic alkali solution and a halogen and continuously collecting a reaction solution containing halogen oxyacid, and an production apparatus of halogen oxyacid, which includes a reactor, a means of supplying an organic alkali solution to the reactor, a means of supplying a halogen to the reactor, and a means of collecting a reaction solution for taking out the reaction solution from the reactor, in which the organic alkali solution and the halogen are continuously supplied by the means of supplying an organic alkali solution and the means of supplying a halogen, respectively, to the reactor so as to be mixed therein such that a solution containing halogen oxyacid is generated as a reaction solution, and the reaction solution is continuously collected by the means of collecting a reaction solution are provided.