A glow plug comprising: a cylindrical metal shell; a ceramic heater provided in a tip end side of said metal shell and including a heating part at a tip end of said ceramic heater; and a centre pole provided in a rear end side of said metal shell, the ceramic heater comprising: a cylindrical substrate comprising an insulator; a resistor provided in one end side of said substrate; a pair of lead parts (12b, 12c) provided in said substrate, connected to said resistor and extending to an opposite end side of said substrate, and a pair of electrode parts (12a, 12d) exposed at a surface of an opposite end side of said substrate and connected respectively to said lead parts (12b, 12c), wherein the pair of electrode parts is provided within the metal shell; wherein both lead parts (12b,12c) are made of the same material as both electrode parts (12a,12d), characterized in that a cross-sectional area of an electrode part in a direction along an axis of said ceramic heater is larger than a cross-sectional area of a lead part (12b, 12c) connected to said electrode part (12a, 12d) in a direction perpendicular to said axis of said ceramic heater, wherein the cross-sectional area of the electrode part in the direction along the axis of the ceramic heater is not larger than two times the cross-sectional area of the lead part connected to the electrode part in the direction perpendicular to the axis of the ceramic heater. a cylindrical metal shell; a ceramic heater provided in a tip end side of said metal shell and including a heating part at a tip end of said ceramic heater; and a centre pole provided in a rear end side of said metal shell, the ceramic heater comprising: a cylindrical substrate comprising an insulator; a resistor provided in one end side of said substrate; a pair of lead parts (12b, 12c) provided in said substrate, connected to said resistor and extending to an opposite end side of said substrate, and a pair of electrode parts (12a, 12d) exposed at a surface of an opposite end side of said substrate and connected respectively to said lead parts (12b, 12c), wherein the pair of electrode parts is provided within the metal shell; wherein both lead parts (12b,12c) are made of the same material as both electrode parts (12a,12d), characterized in that a cross-sectional area of an electrode part in a direction along an axis of said ceramic heater is larger than a cross-sectional area of a lead part (12b, 12c) connected to said electrode part (12a, 12d) in a direction perpendicular to said axis of said ceramic heater, wherein the cross-sectional area of the electrode part in the direction along the axis of the ceramic heater is not larger than two times the cross-sectional area of the lead part connected to the electrode part in the direction perpendicular to the axis of the ceramic heater. a cylindrical substrate comprising an insulator; a resistor provided in one end side of said substrate; a pair of lead parts (12b, 12c) provided in said substrate, connected to said resistor and extending to an opposite end side of said substrate, and a pair of electrode parts (12a, 12d) exposed at a surface of an opposite end side of said substrate and connected respectively to said lead parts (12b, 12c), wherein the pair of electrode parts is provided within the metal shell; wherein both lead parts (12b,12c) are made of the same material as both electrode parts (12a,12d), characterized in that a cross-sectional area of an electrode part in a direction along an axis of said ceramic heater is larger than a cross-sectional area of a lead part (12b, 12c) connected to said electrode part (12a, 12d) in a direction perpendicular to said axis of said ceramic heater, wherein the cross-sectional area of the electrode part in the direction along the axis of the ceramic heater is not larger than two times the cross-sectional area of the lead part connected to the electrode part in the direction perpendicular to the axis of the ceramic heater.