The invention relates to a scanner's optical device, for receiving the light coming from the image of an object being scanned, comprising: several reflective mirrors, a light-focusing module, and a charge coupled device. The reflective mirrors provide reflection and directional change for the light and, by appropriately arranging several reflective mirrors, the light of the object being scanned directionally changed to a predetermined route. With at least one curving mirror, the light-focusing module focuses the light of the predetermined route and then directionally changes it, and a raster is then provided in the light route of the curving mirror for filtering out unnecessary light. The charge coupled device receives the light coming from the light-focusing module and converts it into electronic signals. The said light-focusing module replaces the prior art lens set for executing a scanning job.