A glow plug including a heater (200) having a rear heat-generating element (260) formed of a resistance heat-generating element, and provided in an axial region thereof between a forward end (136) of a housing and a rear end (315) of a displacement member (300) located rearward of the forward end (136). The heat-generating element (260) is arranged separately from a forward heat-generating element (205) provided at a forward end portion of the heater.