PROBLEM TO BE SOLVED: To provide a plant growth regulator that has long persistence of ethylene activity and shows non-gaseous ethylene activity with spray easiness.SOLUTION: A plant growth regulator comprises a compound represented by the following general formula (I) [where R, R, Rand Reach represent a methyl group and others, Rrepresents a 5-dimethylaminonaphthalene-1-yl group and others, and n represents an integer of 1 and others] or salt thereof as an active ingredient.SELECTED DRAWING: None