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 X1 represents CH or N; any one of X2, X3 and X4 represents N, and the others represent CH; any one or two of Y1, Y2, Y3 and Y4 represent C—R4, and the others are the same or different and represent CH or N; R1 represents an optionally substituted monocyclic or bicyclic unsaturated heterocyclic group having 1 to 4 heteroatoms selected from N, S and O; R2 represents an alkyl group having 1 to 6 carbon atoms, or the like; and R3 and R4 represent —CO—R5 or the like.