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 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 (O) of the glow plug , with a cross section which is a rearmost one of cross sections of the heat generation element appearing in the fusion zone on one side of the axial line (O) and which is disposed at least partially within the fusion zone being defined as a first heat-generation-element cross section , with a forwardmost one of cross sections of the heat generation element appearing externally of the fusion zone on the one side of the axial line (O) being defined as a second heat-generation-element cross section , and with a cross section which is one of the cross sections of the heat generation element appearing externally of the fusion zone on the one side of the axial line (O) and which is located immediately rearward of the second heat-generation-element cross section being defined as a third heat-generation-element cross section , characterised in that a distance A in the direction of the axial line (O) between a rearmost end of the first heat-generation-element cross section and a forwardmost end of the second heat-generation-element cross section is greater than a distance B in the direction of the axial line (O) between a rearmost end of the second heat-generation-element cross section and a forwardmost end of the third heat-generation-element cross section . 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 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 (O) of the glow plug , with a cross section which is a rearmost one of cross sections of the heat generation element appearing in the fusion zone on one side of the axial line (O) and which is disposed at least partially within the fusion zone being defined as a first heat-generation-element cross section , with a forwardmost one of cross sections of the heat generation element appearing externally of the fusion zone on the one side of the axial line (O) being defined as a second heat-generation-element cross section , and with a cross section which is one of the cross sections of the heat generation element appearing externally of the fusion zone on the one side of the axial line (O) and which is located immediately rearward of the second heat-generation-element cross section being defined as a third heat-generation-element cross section , characterised in that a distance A in the direction of the axial line (O) between a rearmost end of the first heat-generation-element cross section and a forwardmost end of the second heat-generation-element cross section is greater than a distance B in the direction of the axial line (O) between a rearmost end of the second heat-generation-element cross section and a forwardmost end of the third heat-generation-element cross section . <EOS>