A spark plug, comprising: an insulator that has a through hole extending in a direction of an axial line; a center electrode at least partially inserted into a front end side of the through hole; a terminal metal fitting at least partially inserted into a rear end side (D1r) of the through hole; and a connecting portion electrically connecting the center electrode and the terminal metal fitting together within the through hole, wherein the connecting portion includes a resistor element, the resistor element includes an aggregate (Aa), a filler (P1, P2) containing ZrO 2, and carbons, and the spark plug being characterized by a cross section including the axial line of the resistor element, where: a center line is defined by the axial line, a target region is defined by a rectangular region where a size in a direction perpendicular to the axial line is 1800 μm and a size in a direction of the axial line is 2400 μm; a transverse line-shaped region (L01 to L12) is defined by a line-shaped region, the line-shaped region being constituted of nine square regions arranged in the direction perpendicular to the axial line in the case where the target region is divided into a plurality of square regions, the square region having a length of 200 μm on a side; a first type region is defined by a square region where a proportion of an area of ZrO 2 is 25% or more; and a second type region is defined by a square region where a proportion of an area of ZrO 2 is less than 25%, a total number of the transverse line-shaped regions (L01 to L12) including two or more of the first type regions is equal to or more than 5. an insulator that has a through hole extending in a direction of an axial line; a center electrode at least partially inserted into a front end side of the through hole; a terminal metal fitting at least partially inserted into a rear end side (D1r) of the through hole; and a connecting portion electrically connecting the center electrode and the terminal metal fitting together within the through hole, wherein the connecting portion includes a resistor element, the resistor element includes an aggregate (Aa), a filler (P1, P2) containing ZrO 2, and carbons, and the spark plug being characterized by a cross section including the axial line of the resistor element, where: a center line is defined by the axial line, a target region is defined by a rectangular region where a size in a direction perpendicular to the axial line is 1800 μm and a size in a direction of the axial line is 2400 μm; a transverse line-shaped region (L01 to L12) is defined by a line-shaped region, the line-shaped region being constituted of nine square regions arranged in the direction perpendicular to the axial line in the case where the target region is divided into a plurality of square regions, the square region having a length of 200 μm on a side; a first type region is defined by a square region where a proportion of an area of ZrO 2 is 25% or more; and a second type region is defined by a square region where a proportion of an area of ZrO 2 is less than 25%, a total number of the transverse line-shaped regions (L01 to L12) including two or more of the first type regions is equal to or more than 5. a center line is defined by the axial line, a target region is defined by a rectangular region where a size in a direction perpendicular to the axial line is 1800 μm and a size in a direction of the axial line is 2400 μm; a transverse line-shaped region (L01 to L12) is defined by a line-shaped region, the line-shaped region being constituted of nine square regions arranged in the direction perpendicular to the axial line in the case where the target region is divided into a plurality of square regions, the square region having a length of 200 μm on a side; a first type region is defined by a square region where a proportion of an area of ZrO 2 is 25% or more; and a second type region is defined by a square region where a proportion of an area of ZrO 2 is less than 25%, a total number of the transverse line-shaped regions (L01 to L12) including two or more of the first type regions is equal to or more than 5.