An image reading device comprising: a housing ; a document loading surface being provided at a top part of the housing and loading a document thereon; a reading unit being arranged below the document loading surface , being movable in a horizontal direction along the document loading surface in the housing , and optically reading an image of the document loaded on the document loading surface ; a first through hole being provided in a manner such as to be pierced through the housing ; a second through hole being provided oppositely to the first through hole in a manner such as to be pierced through the reading unit located at a predefined place; an insertion member stopping movement of the reading unit in the horizontal direction and fixing the reading unit in the housing , when being inserted in the first through hole and the second through hole ; a first member closing the first through hole and having a shape deforming in accordance with the insertion of the insertion member in the first through hole and the second through hole , an elastic member closing the first through hole and being extendable in an insertion direction of the insertion member is provided as the first member, and the elastic member has a shape not entering the second through hole of the reading unit before the insertion of the insertion member , upon the insertion of the insertion member in the insertion direction, the elastic member is deformed along a shape of the insertion member into a shape entering the second through hole of the reading unit , and upon removal of the insertion member from the first through hole and the second through hole , the elastic member is restored into the shape, before the insertion, not entering the second through hole . a housing ; a document loading surface being provided at a top part of the housing and loading a document thereon; a reading unit being arranged below the document loading surface , being movable in a horizontal direction along the document loading surface in the housing , and optically reading an image of the document loaded on the document loading surface ; a first through hole being provided in a manner such as to be pierced through the housing ; a second through hole being provided oppositely to the first through hole in a manner such as to be pierced through the reading unit located at a predefined place; an insertion member stopping movement of the reading unit in the horizontal direction and fixing the reading unit in the housing , when being inserted in the first through hole and the second through hole ; a first member closing the first through hole and having a shape deforming in accordance with the insertion of the insertion member in the first through hole and the second through hole , an elastic member closing the first through hole and being extendable in an insertion direction of the insertion member is provided as the first member, and the elastic member has a shape not entering the second through hole of the reading unit before the insertion of the insertion member , upon the insertion of the insertion member in the insertion direction, the elastic member is deformed along a shape of the insertion member into a shape entering the second through hole of the reading unit , and upon removal of the insertion member from the first through hole and the second through hole , the elastic member is restored into the shape, before the insertion, not entering the second through hole . <EOS>