Abstract: Disclosed herewith is an optical axis displacement sensor, which has a convex lens having a hole on the optical axis, a light shielding plate having a hole on the optical axis and two parallel straight slits, a laser light source for irradiating a laser beam on a target surface through the holes of the light shielding plate and the convex lens, a CCD line sensor provided in parallel to the light shielding plate, perpendicular to the optical axis and perpendicular to the two straight slits, a cylindrical lens provided between the light shielding plate and the CCD line sensor, and a calculation unit for calculating the displacement of the target surface from the focal point of the convex lens, using the output of the CCD line sensor.

Abstract: A first convex lens, having a focal length f1 and a second convex lens, having a focal length f2, are arranged at an interval d (=f1+f2). A mirror is provided, on the optical axis, to reflect the laser beam from a laser thereby emitting parallel beams, through the first lens, onto the surface to be measured. The interval between the first lens and the surface is f1+z1. The interval between the second lens and the image point, at which the image of the surface is formed, is f2+z2. A position detector of this point, comprises a slit plate, a third convex lens, having a focal length f3, and a CCD line sensor. The interval between the slit plate and the sensor is l.sub.0. The second and third lenses are so arranged that the focal points coincide. The slit plate is provided perpendicular to the optical axis, immediately before the third lens, and a pin hole is opened at an interval d.sub.0 on either side of the optical axis. The line sensor is positioned in parallel with the slit plate.