Provided are: active AREB1 capable of improving plant tolerance against environmental stresses such as drought, salt, and low temperature through expression at high levels in plant bodies; and a method for improving plant environmental stress tolerance using the active AREB1. Also provided is an active environmental stress responsive transcription factor AREB1 gene lacking the activation control region of the plant environmental stress responsive transcription factor AREB1 and containing an N-terminal transcriptional activation domain and a DNA binding domain.