A scan assisting fixing device and a scanner using the same are provided. The fixing device is for fixing an object to be scanned, which includes a scanning portion and a holding portion. The fixing device includes an accommodation region, a scan window and a protrusion portion. When the holding portion is loaded in the accommodation region, the scanning portion correspondingly disposed in the scan window is retained and fixed by the protrusion portion, and the position of the holding portion in the fixing device is constant, so that the scanning portion is always within the range of the field depth of the scanner regardless of the specification of the positive film holder, and the clarity of the scanned image is assured.