A glow plug comprising: a closed-bottomed tube extending in a direction of an axial line (O); a forward coil and a rearward coil disposed within the tube ; and an axial rod connected to a rear end of the rearward coil ; wherein the forward coil is connected at its forward end to a forward end portion of the tube the rearward coil is connected at its forward end to a rear end of the forward coil and has a resistance ratio R1 lower than a resistance ratio R2 of the forward coil , where the resistance ratio R1 is the ratio of a resistance of the rearward coil at 1,000°C to a resistance of the rearward coil at 20°C, and the resistance ratio R2 is the ratio of a resistance of the forward coil at 1,000°C to a resistance of the forward coil at 20°C; characterized in that the forward coil contains Tungsten or Molybdenum as a main component, and in that the tube has a tube forward portion ranging from the forward end of the tube to a position around a center of the forward coil with respect to the direction of the axial line (O), and a tube rearward portion ranging from a position around the rear end of the rearward coil to a position around the forward end of the rearward coil ; and a wall thickness A of the tube forward portion is 0.5 mm or more, a wall thickness B of the tube rearward portion is 0.3 mm or more, and a minimal wall thickness B1 of the tube rearward portion is smaller than the wall thickness A of the tube forward portion . a closed-bottomed tube extending in a direction of an axial line (O); a forward coil and a rearward coil disposed within the tube ; and an axial rod connected to a rear end of the rearward coil ; wherein the forward coil is connected at its forward end to a forward end portion of the tube the rearward coil is connected at its forward end to a rear end of the forward coil and has a resistance ratio R1 lower than a resistance ratio R2 of the forward coil , where the resistance ratio R1 is the ratio of a resistance of the rearward coil at 1,000°C to a resistance of the rearward coil at 20°C, and the resistance ratio R2 is the ratio of a resistance of the forward coil at 1,000°C to a resistance of the forward coil at 20°C; characterized in that the forward coil contains Tungsten or Molybdenum as a main component, and in that the tube has a tube forward portion ranging from the forward end of the tube to a position around a center of the forward coil with respect to the direction of the axial line (O), and a tube rearward portion ranging from a position around the rear end of the rearward coil to a position around the forward end of the rearward coil ; and a tube forward portion ranging from the forward end of the tube to a position around a center of the forward coil with respect to the direction of the axial line (O), and a tube rearward portion ranging from a position around the rear end of the rearward coil to a position around the forward end of the rearward coil ; and a wall thickness A of the tube forward portion is 0.5 mm or more, a wall thickness B of the tube rearward portion is 0.3 mm or more, and a minimal wall thickness B1 of the tube rearward portion is smaller than the wall thickness A of the tube forward portion . <EOS>