To sensitize the response of the acceleration of an objective lens with respect to a driving force by driving a uniaxial actuator part connected to a slider with an elastic body to simplify a mechanism and to make a driving part light in weight.

First and second tracking driving coils 11, 12 act with a magnetic flux in accordance with a driving current to drive a second carriage 8 in the direction of first and second shafts 1, 2. The second carriage 8 is supported by first and second fine adjusting springs 9, 10 moveabaly in the axial direction of the shafts 1, 2 with respect to a first carriage 7. Consequently, when the relative displacement of the second carriage 8 with respect to the first carriage 7 is within a prescribed range, the second carriage 8 receives only the restoring force in accordance with the relative displacement in the direction of the shafts 1, 2 by the fine adjusting springs 9, 10 and is moved without friction. Then, the response characteristic of the acceleration of an objective lens 19 with respect to the driving force shows a linear response.