Aglow plug comprising: a ceramic heater extending in an axial direction and having a columnar substrate formed of electrically insulating ceramic, a resistance heat-generating element integrated with the substrate and performing resistance heat generation through application of electricity thereto, and an electrode lead-out portion (16, 17) electrically connected to the resistance heat-generating element and formed at a rear end portion of the resistance heat-generating element in such a manner as to be exposed at an outer surface of the substrate; a holding sleeve made of metal, connected directly or indirectly to the electrode lead-out portion (16, 17), and holding the ceramic heater while allowing a forward portion of the ceramic heater to protrude therefrom; a housing having a tubular form and accommodating therein the ceramic heater and the holding sleeve; wherein a heat-generating main portion is located forward of the holding sleeve, where the heat-generating main portion is a forward end portion of the ceramic heater which encompasses a forward end of the ceramic heater; characterized by: a movable member formed of a metal sheet, joined to the holding sleeve and the housing to airtightly separate a forward side and a rear side thereof, and being elastically deformable in response to combustion pressure; and a pressure sensor disposed rearward of the ceramic heater, the holding sleeve and the movable member and in the interior of the housing and adapted to detect pressure applied thereto; and in that: the electrical resistance of the heat-generating main portion accounts for 75% of a total resistance of the ceramic heater, and the cross-sectional area of the heat-generating resistor in the heat-generating main portion is 90% to 110% of the cross-sectional area of the heat-generating resistor in a portion other than the heat-generating main portion, and the heat-generating resistor in the heat-generating main portion is greater in specific resistance than the heat-generating resistor in a portion other than the heat-generating main portion. a ceramic heater extending in an axial direction and having a columnar substrate formed of electrically insulating ceramic, a resistance heat-generating element integrated with the substrate and performing resistance heat generation through application of electricity thereto, and an electrode lead-out portion (16, 17) electrically connected to the resistance heat-generating element and formed at a rear end portion of the resistance heat-generating element in such a manner as to be exposed at an outer surface of the substrate; a holding sleeve made of metal, connected directly or indirectly to the electrode lead-out portion (16, 17), and holding the ceramic heater while allowing a forward portion of the ceramic heater to protrude therefrom; a housing having a tubular form and accommodating therein the ceramic heater and the holding sleeve; wherein a heat-generating main portion is located forward of the holding sleeve, where the heat-generating main portion is a forward end portion of the ceramic heater which encompasses a forward end of the ceramic heater; characterized by: a movable member formed of a metal sheet, joined to the holding sleeve and the housing to airtightly separate a forward side and a rear side thereof, and being elastically deformable in response to combustion pressure; and a pressure sensor disposed rearward of the ceramic heater, the holding sleeve and the movable member and in the interior of the housing and adapted to detect pressure applied thereto; a movable member formed of a metal sheet, joined to the holding sleeve and the housing to airtightly separate a forward side and a rear side thereof, and being elastically deformable in response to combustion pressure; and a pressure sensor disposed rearward of the ceramic heater, the holding sleeve and the movable member and in the interior of the housing and adapted to detect pressure applied thereto; and in that: the electrical resistance of the heat-generating main portion accounts for 75% of a total resistance of the ceramic heater, and the cross-sectional area of the heat-generating resistor in the heat-generating main portion is 90% to 110% of the cross-sectional area of the heat-generating resistor in a portion other than the heat-generating main portion, and the heat-generating resistor in the heat-generating main portion is greater in specific resistance than the heat-generating resistor in a portion other than the heat-generating main portion. the electrical resistance of the heat-generating main portion accounts for 75% of a total resistance of the ceramic heater, and the cross-sectional area of the heat-generating resistor in the heat-generating main portion is 90% to 110% of the cross-sectional area of the heat-generating resistor in a portion other than the heat-generating main portion, and the heat-generating resistor in the heat-generating main portion is greater in specific resistance than the heat-generating resistor in a portion other than the heat-generating main portion.