The present invention provides a fused ring compound of the following
formula [I]
##STR1##
wherein each symbol is as defined in the specification, a pharmaceutically
acceptable salt thereof, and a therapeutic agent for hepatitis C, which
contains this compound. The compound of the present invention shows an
anti-hepatitis C virus (HCV) action based on the HCV polymerase inhibitory
activity, and is useful as a therapeutic agent or prophylactic agent for
hepatitis C.
