The present invention provides a scanner including a housing defining two mounting holes. An elastic rib is located beside each of the two mounting holes to provide a retaining action. A paper cover is pivotally mounted on the housing and has two locking hooks. Each locking hook is mounted in a respective mounting hole of the housing. Thus, the height of the paper cover can be adjusted according to the variation of depth of the locking hook in the mounting hole. In addition, the locking hook is retained by the elastic rib and the catch plate of the mounting hole, such that the paper cover cannot be removed easily, thereby preventing the paper cover from being lost.