The present invention provides a method for promoting plant growth, which comprises treating a plant with at least one compound selected from a group consisting of a compound represented by the following Formula (1): and an agriculturally acceptable salt thereof, provided that a method for promoting plant growth which comprises treating plants with a compound corresponding to any one of the following (1) to (5) and an agriculturally acceptable salt thereof is excluded: (1) 4-(Trifluoromethyl)benzo[b]thiophene-2-carboxylic acid, (2) 5-(Trifluoromethyl)benzo[b]thiophene-2-carboxylic acid, (3) 6-(Trifluoromethyl)benzo[b]thiophene-2-carboxylic acid, (4) 7-(Trifluoromethyl)benzo[b]thiophene-2-carboxylic acid, and (5) Benzo[b]thiophene-2-carboxylic acid.