PURPOSE: To judge the state of a lead ideally by predicting the surface to be formed by a lead which is grounded to a surface where parts are placed as a virtual plane and then inspecting the state of the lead based on it.

CONSTITUTION: The x, y, and z coordinates of each lead L are obtained by measuring a stand-off s which is the distance between the lower surface of a point w of a lead L and that of a package p. Then, the planes of a number of triangles which are constituted by three leads L (w point) is used as first candidates, these are compared with the coordinates of the leads L, and a candidate surface where the first candidate surfaces are positioned at the lower sides of all leads L are selected as second candidate surfaces. Then, when the intersection between the vertical line passing through the center of gravity of parts and the second candidate surface is located inside the triangle which is formed by three leads L, it becomes a virtual plane. The virtual plane indicates the plane of a stand when parts are placed on a flat stand, etc., and the state of the leads L when the parts are placed on a flat surface can be recognized by calculating the distance between the virtual plane and the leads L.