Solid titanium catalyst component, olefin polymerization catalyst, and olefin polymerization process

A solid titanium catalyst component (I) comprising titanium, magnesium, halogen, a cyclic ester compound (a) represented by the following formula (1) and a cyclic ester compound (b) represented by the following formula (2):

• wherein n is an integer of 5 to 10,
• R2 and R3 are each independently COOR1 or R, at least one of R2 and R3 is COOR1, and a single bond (except Ca—Ca bond, and Ca—Cb bond in the case where R3 is R) in the cyclic skeleton may be replaced with a double bond,
• R1 is each independently a monovalent hydrocarbon group of 1 to 20 carbon atoms,
• plural R are each independently an atom or a group selected from a hydrogen atom, a hydrocarbon group of 1 to 20 carbon atoms, a halogen atom, a nitrogen-containing group, an oxygen-containing group, a phosphorous-containing group, a halogen-containing group and a silicon-containing group, and they may be bonded to one another to from a ring, but at least one R is not a hydrogen atom, and
• in a skeleton of the ring formed by bonding of plural R to one another may be contained a double bond, and when two or more Ca to each of which COOR1 is bonded are contained in the skeleton of the ring, the number of carbon atoms to constitute the skeleton of the ring is 5 to 10;
• wherein n is an integer of 5 to 10, and
• R4 and R5 are each independently COOR1 or a hydrogen atom, at least one of R4 and R5 is COOR1, R′ is each independently a monovalent hydrocarbon group of 1 to 20 carbon atoms, and a single bond (except Ca—Ca bond, and Ca—Cb bond in the case where R5 is R) in the cyclic skeleton may be replaced with a double bond.