A plant growth accelerator or an agent for growing vigourous seedlings, which comprises a compound represented by formula (1) as an active ingredient: [wherein R 1 and R 2 each independently represent a C 1-4 alkyl group Y represents a hydrogen atom, a halogeno group, a C 1-4 alkyl group, or a C 1-4 haloalkyl group each R 3 independently represents a halogeno group, a cyano group, a nitro group, a C 1-4 alkyl group or a C 1-4 haloalkyl group and n represents the number of R 3 and is an integer of 0 to 6.]
