To reliably measure a grid face angle by irradiating a laser beam in the in-line direction to a grid by adjusing a focus, averaging plural measured values of a height from a reference surface, and calculating an angle of first and third planes to a second plane by the least square method.

For example, a second grid 4 is constituted so that first and third planes become an inclination of 7 degrees to a second plane, and beam passing holes are juxtaposed and bored in a row in the center of the respective planes. This is installed on a support stand 24 so that the first and the third planes become higher than the second plane. A laser beam emitted by a laser focus displacement gauge 21 is continuously irradiated in the in-line direction in which the beam passing holes are formed, and a distance from the second grid 4 is continuously measured at plural points by moving X-Y stages 22 and 23 by driving parts 35 and 36. These measured values are averaged by a calculating means of a control part 20, and the first to third planes are respectively expressed by straight lines by the least square method, and an angle formed by these straight lines is measured, and an angle of the first and the third planes to the second plane is calculated.