Isoprene polymerization catalyst composition, method for producing synthetic polyisoprene, and syn

An isoprene polymerization catalyst composition includes : Component (a) : a rare earth element compound having a rare earth element-oxygen bond or a rare earth element-sulfur bond; Component (b) : an ionic compound; and Component (c) : at least one compound selected from the group consisting of a compound of formula (X) : YR1aR2bR3c and a compound having a repeating unit of formula (Y) : (—Y(R1)O—) (where Y is a metal selected from groups 1, 2, 12 and 13 in a periodic table, R1 and R2 are C1-10 hydrocarbon groups or hydrogen atoms and R3is a C1-10 hydrocarbon group).