Provided are a treatment device and a treatment method capable of easily reusing a used rinsing liquid, and reducing the amount of waste liquid. A treatment device has: a developing portion which is provided with a developing unit which performs development by removing a non-exposed portion of a flexographic printing plate precursor after imagewise exposure using a developer containing a washing solution; a rinsing portion which is provided with a rinsing liquid supply portion which supplies a rinsing liquid containing substantially only water as a component to at least a surface of the flexographic printing plate precursor after development, from which the non-exposed portion of the flexographic printing plate precursor has been removed; a developer storage portion which has a developer storage tank which stores the developer which is used for the development in the developing portion; a first liquid feeding path through which the developer after development is fed to the developer storage tank of the developer storage portion; and a second liquid feeding path different from the first liquid feeding path, through which the rinsing liquid supplied by the rinsing portion is fed to the developer storage tank of the developer storage portion, and the developing portion repeatedly uses the developer stored in the developer storage tank of the developer storage portion to perform the development.