It is made possible to efficiently produce adamantane and analogues thereof, namely a hydrocarbon having an adamantane structure by a process which comprises isomerizing a tricyclic saturated hydrocarbon having ten or more carbon atoms in the presence of a solid-acid catalyst containing one or two or more metals selected from among the metals belonging to group VIII in the Periodic Table (group 8 to 12 in the new Periodic Table), wherein one or two or more monocyclic saturated hydrocarbons are added to the tricyclic saturated hydrocarbon having ten or more carbon atoms.