A scanner includes a housing, a transparent platform installed on the housing, a shaft installed inside the housing, and a scanning module installed inside the housing and on the shaft in a movable manner. The scanning module comprises a sensing module for scanning a document on the transparent platform and transforming it into digital signal and a sensor carriage. The sensor carriage comprises a base for carrying the sensing module, and a buffer pad connected to the base in a rotatable manner for contacting the transparent platform and fixing the sensing module in the sensor carriage.