When Z represents a heterocyclic thio group, the moiety of the heterocyclic group is a 3- to 12-membered, and preferably 5- or 6-membered, substituted or unsubstituted, saturated or unsaturated, and monocyclic or condensed ring heterocyclic group having from 1 to 20, and preferably from 1 to 10 carbon atoms and including at least one nitrogen, oxygen, and sulfur atom as the heteroatom.