A rubber ring for a gasket has a first bulging portion composing a seal portion; a second bulging portion composing an attachment portion; and a depressed portion between the first bulging portion and the second bulging portion. The first bulging portion includes a thickest portion carrying out a sealing function, and when the rubber ring is compressed from both sides, the second bulging portion and the depressed portion have a thickness which does not contact with the faces sandwiching the gasket. An end of the metal plate is positioned in a range of the depressed portion between the first bulging portion and the second bulging portion, and between changing points wherein each of slope face, sloping toward the depressed portion from the two bulging portions, changes into a curved surface concaving on an outer side from a curved surface projecting on the outer side.