An image processing apparatus having a structure in which the positioning accuracy of the optical instruments related to image processing are hardly influenced from the condition of the installation surface of the apparatus body. Near the edges of floor plate 60 forming the undersurface of the body of image processing apparatus A, four legs 61, 62, 63a, and 63b are provided in a protruding manner in three points forming generally a triangle, and optical unit X1 in which the optical instruments are mounted is supported by vertical positioning plate 6a or horizontal positioning plate 6a, which are a part of the apparatus body's structure, in three points forming a triangle in the same direction as the triangle formed by Legs 61, 62, and 63 in three points when viewed from underneath, and then, these three points are arranged in the position near each of the three points provided with legs 61, 62, and 63 when viewed from underneath.