PURPOSE: To measure the angle of cutting with high accuracy by obtaining an angle in the direction of a maximum gradient of a lattice plane to the cut surface of a crystal body and an angle of displacement from a reference end face in the direction of the maximum gradient.

CONSTITUTION: A (y) cut plate orthogonal to the (y) axis of crystal axes (x, y, z) is rotated to the left centering around the (z) axis and the (x) axis in a quartz plate. Consequently, a crystal lattice plane is formed in a plane having end-face inclinations α, β in the -x' axis and +z' axis directions to a cut surface. When an angle POP' in the direction P of the maximum gradient (the angle of deviation) of the lattice plane to the cut surface is represented by the maximum angle of deviation α and the angle of displacement in the direction P of the maximum angle of deviation from a reference end face AA' by β at that time, the inclinations θ, β of the crystal lattice plane are shown in θ=tan-1{(1-cos2')1/2.cosβ'/cosα} and =tan-1{1-cos2α)1/2.tanβ'.cosα/ cosβ'} (β' represents β+90° and an angle formed by an axis Q, Q' orthogonal in the direction P and the end face AA') respectively. Accordingly, when the maximum angle of deviation α and the angle of displacement thereof β are acquired, the inclinations α, β can be computed easily.