PURPOSE: To detect a crack an a split at a high speed even if an object to be inspected is not positioned exactly, by deriving a linear peripheral part of a binary-coded picture element data, and scanning a cracked part along this peripheral part.

CONSTITUTION: An image input unit 3 converts an image pickup signal of an object to be inspected which has been brought to an image pickup by an image pickup means 8, to a binary-coded picture element data, and stores it in an image memory 5 as a two-dimensional coordinate data of an XY axis direction. An image display unit 4 displays the image element data on a CRT9, and a program use memory 6 stores a program of a CPU1. Also, based on the picture element data which is stored in the memory 5, a scanning area containing a picture element data of a linear peripheral part for inspecting a crack of the object to be inspected is set. In this scanning area, by deriving a primary linear expression for showing the linear peripheral part, an intersection of each adjacent primary expression is calculated, a coordinate of the picture element data in the vicinity of the intersection is set as a start point and an end point of a scan of a crack inspection of the linear peripheral part, the picture element data is scanned along the primary linear expression at a prescribed picture element interval in the X axis and Y axis directions, and a cracked part is detected.