A glow plug (10, 70) comprising: a tube (40, 71) extending in a direction of an axial line and having a closed front end; a front coil (51, 81) disposed in the tube (40, 71) and having a front end which is electrically connected to a front end portion (41, 72) of the tube (40, 71), the front coil (51, 81) generating heat by being electrically energized; a rear coil (52, 82) disposed in the tube (40, 71) and disposed rearward of the front coil (51, 81) so as to be electrically connected to the front coil (51, 81); and insulating powder sealed in the tube (40, 71), characterized in that: a relationship is established where a median diameter of particle diameters of the insulating powder disposed around the front coil (51, 81) and disposed within a first region (46, 74) is larger than a median diameter of particle diameters of the insulating powder disposed around the rear coil (52, 82) and disposed within a second region (47, 75), the first region (46, 74) being a part in the direction of the axial line of the tube (40, 71) and including a maximally heat-generating portion (45, 73) at which a temperature of a surface of the tube (40, 71) reaches a maximum temperature, the second region (47, 75) being a part in the direction of the axial line of the tube (40, 71), wherein: in a particle size distribution of the insulating powder disposed within the first region (46, 74), a cumulative value of frequencies of particle diameters not smaller than 60 μm is not lower than 1.0%, and wherein: in a particle size distribution of the insulating powder disposed within the second region (47, 75), frequencies of particle diameters not smaller than 60 μm are 0%. a tube (40, 71) extending in a direction of an axial line and having a closed front end; a front coil (51, 81) disposed in the tube (40, 71) and having a front end which is electrically connected to a front end portion (41, 72) of the tube (40, 71), the front coil (51, 81) generating heat by being electrically energized; a rear coil (52, 82) disposed in the tube (40, 71) and disposed rearward of the front coil (51, 81) so as to be electrically connected to the front coil (51, 81); and insulating powder sealed in the tube (40, 71), characterized in that: a relationship is established where a median diameter of particle diameters of the insulating powder disposed around the front coil (51, 81) and disposed within a first region (46, 74) is larger than a median diameter of particle diameters of the insulating powder disposed around the rear coil (52, 82) and disposed within a second region (47, 75), the first region (46, 74) being a part in the direction of the axial line of the tube (40, 71) and including a maximally heat-generating portion (45, 73) at which a temperature of a surface of the tube (40, 71) reaches a maximum temperature, the second region (47, 75) being a part in the direction of the axial line of the tube (40, 71), wherein: in a particle size distribution of the insulating powder disposed within the first region (46, 74), a cumulative value of frequencies of particle diameters not smaller than 60 μm is not lower than 1.0%, and wherein: in a particle size distribution of the insulating powder disposed within the second region (47, 75), frequencies of particle diameters not smaller than 60 μm are 0%.