Provided is a high-value added fertilizer using a microorganism or a component of a microorganism and especially a fertilizer capable of promoting the bearing of fruit trees and fruit vegetables. A reducing fertilizer obtained by subjecting a mixture of a microorganism or a component of a microorganism with phosphoric acid component and/or potassium component to a hydrothermal reaction treatment is capable of promoting the growth the roots, especially, the root hairs of fruit trees and also promoting the enlargement of their fruits. In particular, because of the reducing characteristic, the reducing fertilizer of the present invention has an excellent affinity for cells constituting the roots, and enables phosphoric acid component and potassium component, which are useful fertilizer components, to be absorbed effectively.