It is intended to provide a novel azabicyclo compound which exhibits both HSP90 inhibitory activity and cell proliferation inhibitory effect. Specifically disclosed is a compound represented by the following general formula (I) or a salt thereof: wherein X 1 represents CH or N； any one of X 2 , X 3 and X 4 represents N, and the others represent CH； any one or two of Y 1 , Y 2 , Y 3 and Y 4 represent C-R 4 , and the others are the same or different and represent CH or N； R 1 represents an optionally substituted monocyclic or bicyclic unsaturated heterocyclic group having 1 to 4 heteroatoms selected from N, S and O； R 2 represents an alkyl group having 1 to 6 carbon atoms, or the like； and R 3 and R 4 represent -CO-R 5 or the like.
