An image forming apparatus includes a space portion for stacking sheets thereon, and is constituted of an image forming portion and an image reading portion including first and second scanning optical systems therein. In the image forming apparatus, the image reading portion is loaded on three points that correspond to both corners on the scanning start position side and one corner on the apparatus rear side. This configuration allows the first and second scanning optical systems to compensate for each other's misalignment, thereby obtaining stable output images.