A glow plug comprising: a tubular member having a tubular shape, said tubular member containing nickel (Ni), a heat-generating element disposed within the tubular member and adapted to generate heat through application of electricity thereto; wherein the heat-generating element is formed primarily of tungsten or molybdenum (Mo), characterized by: a connection portion (830, 830C, 830D, 830F) which includes a forward end fusion zone (832, 832C, 832D, 832F), a rear end fusion zone (831, 831C, 831 D, 831 F) and a portion (835, 835C, 835D, 835F) which remains unfused, wherein the connection portion (830, 830C, 830D, 830F) connects the tubular member and the heat-generating element, and the forward end fusion zone (832, 832C, 832D, 832F) is formed as a result of welding to the tubular member, and the rear end fusion zone (831, 831C, 831 D, 831 F) is formed as a result of welding to the heat-generating element, wherein a portion of the rear end fusion zone (831, 831C, 831 D, 831 F) which extends up to at least 20 μm from an interface with the heat-generating element does not contain nickel (Ni), and the portion (835, 835C, 835D, 835F) which remains unfused contains substantially no nickel (Ni). a tubular member having a tubular shape, said tubular member containing nickel (Ni), a heat-generating element disposed within the tubular member and adapted to generate heat through application of electricity thereto; wherein the heat-generating element is formed primarily of tungsten or molybdenum (Mo), characterized by: a connection portion (830, 830C, 830D, 830F) which includes a forward end fusion zone (832, 832C, 832D, 832F), a rear end fusion zone (831, 831C, 831 D, 831 F) and a portion (835, 835C, 835D, 835F) which remains unfused, wherein the connection portion (830, 830C, 830D, 830F) connects the tubular member and the heat-generating element, and the forward end fusion zone (832, 832C, 832D, 832F) is formed as a result of welding to the tubular member, and the rear end fusion zone (831, 831C, 831 D, 831 F) is formed as a result of welding to the heat-generating element, wherein a portion of the rear end fusion zone (831, 831C, 831 D, 831 F) which extends up to at least 20 μm from an interface with the heat-generating element does not contain nickel (Ni), and the portion (835, 835C, 835D, 835F) which remains unfused contains substantially no nickel (Ni). a connection portion (830, 830C, 830D, 830F) which includes a forward end fusion zone (832, 832C, 832D, 832F), a rear end fusion zone (831, 831C, 831 D, 831 F) and a portion (835, 835C, 835D, 835F) which remains unfused, wherein the connection portion (830, 830C, 830D, 830F) connects the tubular member and the heat-generating element, and the forward end fusion zone (832, 832C, 832D, 832F) is formed as a result of welding to the tubular member, and the rear end fusion zone (831, 831C, 831 D, 831 F) is formed as a result of welding to the heat-generating element, wherein a portion of the rear end fusion zone (831, 831C, 831 D, 831 F) which extends up to at least 20 μm from an interface with the heat-generating element does not contain nickel (Ni), and the portion (835, 835C, 835D, 835F) which remains unfused contains substantially no nickel (Ni).