Abstract: The present invention provides a displacement detection apparatus uses short scales and can provide a long measurable range comparable to a single long scale with a short bed length.

Abstract: The present invention provides a displacement detection apparatus uses short scales and can provide a long measurable range comparable to a single long scale with a short bed length.

Abstract: A displacement measurement apparatus utilizing an astigmatism, comprises an objective lens, an optical system detecting an offset distance between a relative distance of the objective lens to a measured surface and its focal distance by utilizing a reflection beam from the measured surface, to generate a focus-error signal, an actuator connected to the lens for moving the objective lens in a direction of an optical axis of the lens on the basis of the focus-error signal, so that the relative distance is maintained at the focal distance, and a linear scale and a detecting head cooperative with each other for detecting a displacement of the linear scale to the head. One of the linear scale and the head is integrally connected to the actuator for moving together with the lens and coaxially aligned with the optical axis, and the other is stationary.