PURPOSE: To speedily stop a positioning servo element by stopping movement of an objective lens in response to a control signal from an excessive error means when the error signal of a servo means exceeds a threshold value.

CONSTITUTION: When a focusing servo circuit 22 detects out-of-focus or unwanted focusing state, an amplifier 28 is activated and a signal for switching from a mutual conductance mode to a voltage amplification mode is supplied through an OR circuit 34. When unwanted speed is detected, a positioning servo circuit 24 similarly generates the signal through a line 33. The signal on the line 33 is transmitted through the circuit 34 to an amplifier 28. In a voltage amplify mode, the amplifier 28 dynamically controls a rough moving actuator 30. The circuits 22 and 24 are started by a signal supplied from another control circuit 40.