There are provided a washout processor and a washing method that prevent solid contents from being attached to a developed flexographic printing plate precursor again. A washout processor that develops an imagewise exposed flexographic printing plate precursor using a washing solution includes a developing tank that is filled with the washing solution, a development unit that performs the development by removing a non-exposed portion of the flexographic printing plate precursor using the washing solution in the developing tank, and a flow creation unit that flows the washing solution in at least one region of a first region where the flexographic printing plate precursor is carried into the washing solution of the developing tank or a second region where the flexographic printing plate precursor is carried out from the washing solution of the developing tank, in an intersecting direction to cross a width of the flexographic printing plate precursor with respect to a traveling direction of the flexographic printing plate precursor.