A printer, comprising: a main body cover, wherein the main body cover is configured to house a roll paper and has an upper portion, the upper portion having an opening through which the roll paper can be loaded; and an upper cover configured to close the opening of the upper portion of the mainbody cover, a discharge port arranged between the mainbody cover and the upper cove at a front side of the main body cover, wherein the upper cover and the main body cover constitute a gap at a back side of the main body cover, characterized in that the main body cover has: a rectangular protrusion arranged on an inner surface of an upper end of the back side in a direction orthogonal to an axial direction of the roll paper; a rib-shaped protrusion arranged on an upper end of the back side protruding in the direction orthogonal to the axial direction of the roll paper; or a protrusion arranged on an upper end of the back side having a peak extending from the backside to the direction orthogonal to the axial direction of the roll paper, wherein the upper cover has a recess arranged on an edge portion of the back side that interfaces with the protrusion and provides with the protrusion a gap included in the gap between the main body cover and the upper cover, wherein the gap comprises at least one portion extending in a direction intersecting with the axial direction of the roll paper housed in the main body cover. a main body cover, wherein the main body cover is configured to house a roll paper and has an upper portion, the upper portion having an opening through which the roll paper can be loaded; and an upper cover configured to close the opening of the upper portion of the mainbody cover, a discharge port arranged between the mainbody cover and the upper cove at a front side of the main body cover, wherein the upper cover and the main body cover constitute a gap at a back side of the main body cover, characterized in that the main body cover has: a rectangular protrusion arranged on an inner surface of an upper end of the back side in a direction orthogonal to an axial direction of the roll paper; a rib-shaped protrusion arranged on an upper end of the back side protruding in the direction orthogonal to the axial direction of the roll paper; or a protrusion arranged on an upper end of the back side having a peak extending from the backside to the direction orthogonal to the axial direction of the roll paper, a rectangular protrusion arranged on an inner surface of an upper end of the back side in a direction orthogonal to an axial direction of the roll paper; a rib-shaped protrusion arranged on an upper end of the back side protruding in the direction orthogonal to the axial direction of the roll paper; or a protrusion arranged on an upper end of the back side having a peak extending from the backside to the direction orthogonal to the axial direction of the roll paper, wherein the upper cover has a recess arranged on an edge portion of the back side that interfaces with the protrusion and provides with the protrusion a gap included in the gap between the main body cover and the upper cover, wherein the gap comprises at least one portion extending in a direction intersecting with the axial direction of the roll paper housed in the main body cover.