The present invention provides a novel compound having an excellent antitumor effect, stability and metabolic stability. The compound of the present invention is represented by the following general formula (1) wherein R1 represents a halogen atom, an aryl group, an aryloxy group or a lower alkyl group optionally substituted with one or more halogen atoms； R2 represents a hydrogen atom, a halogen atom, a lower alkyl group or a lower alkoxy group； and； m represents an integer of 1 to 3； provided that when m represents 2 or 3, R1s are the same or different.
