A glow plug (10), comprising: a heating unit (820); and a sheath tube (810) including a tube portion (860) and a welded portion (850), the tube portion (860) being disposed at an outer circumference of the heating unit (820) and extending in an axial direction, the welded portion (850) containing at least a main constituent of the tube portion (860) and a main constituent of the heating unit (820) and closing a front end of the tube portion (860), wherein at least one of the tube portion (860) and the heating unit (820) contains aluminium, and the welded portion (850) contains aluminium at a content ratio of less than 5 % by mass at a part near a boundary with the tube portion (860).