A lens displacing mechanism for an objective lens comprising an actuator movable to displace the objective lens, and a shaped memory alloy (abbreviated to SMA) wire which when heated contracts to a memorized shape to move the actuator to displace the objective lens, is characterized in that the SMA wire has opposite ends that are fixed in place and an intermediate movable portion between the opposite ends that directly contacts the actuator to move the actuator when the SMA wire is heated to contract.