hosphate esters (B1), the particularly preferred include plasticizers indicated by the general formula (5) in which R is a phenyl group, an alkylphenyl group or a phenyl group substituted with ahalogen, and R' is denoted by the general formula (6) below: -Ph'-(A-Ph')p- (6) in the formula (6), Ph' represents a 1,4-phenylene group, p is 0 or 1, and A represents a direct bonding, a methylene group, a