The present invention concerns: a plant growth-promoting agent comprising a compound represented by Formula (I) or a salt thereof:wherein Ar1 represents a substituted or unsubstituted phenyl group, NZ represents a nitrogen-containing heterocyclic ring group or an acyclic nitrogen-containing group having a partial structure of the nitrogen-containing heterocyclic ring group, n is 0, 1, or 2, R1 and R2 each represent a hydrogen atom, a substituted or unsubstituted C1-3-alkyl group, a cyano group, or a carboxyl group, R1 and R2 may together form an oxo group, and when n is 2, R1 or R2 may be the same or different； and a method for promoting plant growth using the plant growth-promoting agent.
