A plug for closing an open end of an open-ended tubular container, comprising: a plug body which includes a press-fit part to be press-fitted into the open end of the tubular container, and a grip part continuous with the top of the press-fit part and having a larger diameter than the press-fit part, wherein an upper surface of the grip part has a recess formed therein and surrounded by an inside wall extending downward; and a cover member including a head plate and a skirt extending downward from a peripheral edge of the head plate, the cover member fitted on the plug body so that a lower surface of the head plate and the upper surface of the grip part of the plug body face each other, wherein an engagement portion provided at the head plate of the cover member and engaged to the inside wall surrounding the recess of the entire plug is extended from the head plate of the cover member to the interior of the recess to face a surface of the inside wall surrounding the recess of the plug body, wherein at least a portion of an inside surface of the head plate of the cover member is engaged against the upper surface of the grip part of the plug body, characterized in that an outer peripheral edge of the grip part of the plug body is located below an outer peripheral edge of the recess in the grip part to thus create a space between the head plate of the cover member and the upper surface of the plug body, and the head plate of the cover member is provided at a portion thereof facing the space with a rib extending in the space downward from the head plate and abutting to the upper surface of the grip part of the plug body. a plug body which includes a press-fit part to be press-fitted into the open end of the tubular container, and a grip part continuous with the top of the a press-fit part to be press-fitted into the open end of the tubular container, and a grip part continuous with the top of the press-fit part and having a larger diameter than the press-fit part, wherein an upper surface of the grip part has a recess formed therein and surrounded by an inside wall extending downward; and wherein an upper surface of the grip part has a recess formed therein and surrounded by an inside wall extending downward; and a cover member including a head plate and a skirt extending downward from a peripheral edge of the head plate, the cover member fitted on the plug body so that a lower surface of the head plate and the upper surface of the grip part of the plug body face each other, wherein an engagement portion provided at the head plate of the cover member and engaged to the inside wall surrounding the recess of the entire plug is extended from the head plate of the cover member to the interior of the recess to face a surface of the inside wall surrounding the recess of the plug body, wherein at least a portion of an inside surface of the head plate of the cover member is engaged against the upper surface of the grip part of the plug body, characterized in that an outer peripheral edge of the grip part of the plug body is located below an outer peripheral edge of the recess in the grip part to thus create a space between the head plate of the cover member and the upper surface of the plug body, and the head plate of the cover member is provided at a portion thereof facing the space with a rib extending in the space downward from the head plate and abutting to the upper surface of the grip part of the plug body.