To provide a method for neutralizing concrete, capable of uniformly neutralizing the surface and space wall surfaces of the applied concrete without relating to the wet or dry state of the concrete.

This method for neutralizing concrete comprises spraying a highly concentrated water-soluble water-repelling agent in a container 4 together with carbon dioxide in a gas cylinder 3 on the surface of the applied concrete 2 by use of a sprayer 5, covering the applied concrete 2 with a sheet, charging carbon dioxide into a space between the applied concrete 2 and the sheet from the gas cylinder 3 and subsequently leaving the charged carbon dioxide for a considerable period (for example, a whole day and night).