A resistor element of a spark plug containing ZrO2, wherein a target region is defined by a rectangular region where the size in the direction perpendicular to an axial line is 1800 μm and the size in the direction of the axial line is 2400 μm. In the case where the target region is divided into a plurality of square regions having lengths of 200 μm on a side, a transverse line-shaped region is defined by a region in a line shape that is constituted of nine square regions arranged in the direction perpendicular to the axial line. A first type region is defined by the square region where a proportion of an area of ZrO2 is 25% or more, and a second type region is defined by the square region where a proportion of an area of ZrO2 is less than 25%.