GLOW PLUG

[Abstract] A rapid temperature increase is achieved while power consumption is suppressed. A glow plug (1) according to the present invention includes a ceramic heater (10) that has a conductive ceramic (11) and an insulating ceramic (16) covering the conductive ceramic (11). The conductive ceramic (11) has: a heat generating section (12) that is arranged at a tip; and a lead (14) that is connected to a rear end of the heat generating section (12). In a cross section that is perpendicular to an axis of the ceramic heater (10), the insulating ceramic (16) has a thinnest portion (16a), where an outer circumferential surface thereof and the heat generating section (12) are closest to each other, in a thickness of 0.5 to 0.7 mm.