A glow plug comprising: a tubular member whose forward end is closed with a fusion zone, and a coiled heat generation element disposed in the tubular member and containing W as a main component, wherein the tubular member has a base metal portion connected to the fusion zone and having a microstructure different from that of the fusion zone; a forward end portion of the heat generation element is inserted into the fusion zone to thereby be joined to the tubular member; and in a cross section of the glow plug taken along an axial line of the glow plug such that the same number of cross sections of the heat generation element appear in the fusion zone on opposite sides of the axial line, characterised by a radial distance F between a radially outermost end of a first heat-generation-element cross section and a radially innermost end of the base metal portion is 0.200 mm or less, the first heat-generation-element cross section being a rearmost one of the cross sections of the heat generation element appearing in the fusion zone on one side of the axial line, the first heat-generation-element cross section being disposed at least partially within the fusion zone, and a radial distance G between a radially outermost end of a second heat-generation-element cross section and a radially innermost end of the base metal portion is 0.200 mm or less, the second heat-generation-element cross section being a rearmost one of the cross sections of the heat generation element appearing in the fusion zone on the other side of the axial line, the second heat-generation-element cross section being disposed at least partially within the fusion zone. a tubular member whose forward end is closed with a fusion zone, and a coiled heat generation element disposed in the tubular member and containing W as a main component, wherein the tubular member has a base metal portion connected to the fusion zone and having a microstructure different from that of the fusion zone; a forward end portion of the heat generation element is inserted into the fusion zone to thereby be joined to the tubular member; and in a cross section of the glow plug taken along an axial line of the glow plug such that the same number of cross sections of the heat generation element appear in the fusion zone on opposite sides of the axial line, characterised by a radial distance F between a radially outermost end of a first heat-generation-element cross section and a radially innermost end of the base metal portion is 0.200 mm or less, the first heat-generation-element cross section being a rearmost one of the cross sections of the heat generation element appearing in the fusion zone on one side of the axial line, the first heat-generation-element cross section being disposed at least partially within the fusion zone, and a radial distance G between a radially outermost end of a second heat-generation-element cross section and a radially innermost end of the base metal portion is 0.200 mm or less, the second heat-generation-element cross section being a rearmost one of the cross sections of the heat generation element appearing in the fusion zone on the other side of the axial line, the second heat-generation-element cross section being disposed at least partially within the fusion zone.