A spark plug includes a metallic shell member having a tubular portion extending along an axial line of the metallic shell, a center electrode disposed inside the tubular portion and extending along the axial line, and a ground electrode which is inserted into an opening 5 provided in the tubular portion and forms a gap between the center electrode and a forward end portion of the round electrode in a direction in which the round electrode extends. A screw thread is provided on an outer circumferential surface of the tubular portion. The opening has a sloping portion which tapers from the outer circumferential surface of the tubular portion toward an inner circumferential surface side. An angle formed between the 10 sloping portion of the opening and a tangent line to the outer circumferential surface is 90 degrees or greater.