PROBLEM TO BE SOLVED: To provide a plant growth promoter that includes minerals derived from sea water by favorable balance, and further includes an organic material that is necessary to a plant, is derived from red algae, and does not exist in a conventional one and a plant growth acceleration method using the same.SOLUTION: A plant growth promoter includes at least one of alkali treatment water after performing alkali treatment to red algae marine algae, and rinse water after performing water washing to the red algae marine algae performed by alkali treatment, and a plant growth acceleration method uses the same. The alkali treatment water and the rinse water are preferably a discharge liquid that is discharged in an agar production in which alkali treatment is performed.
