Spark plug

A spark plug comprising:

• a tubular metallic shell;
• a tubular insulator held in the metallic shell and having an axial hole extending in an axial direction;
• a center electrode held at one end of the axial hole;
• a metallic terminal member held at the other end of the axial hole;
• a resistor element disposed between the center electrode and the metallic terminal member in the axial hole and containing glass and an electrically conductive material;
• and
• two seal members between which the resistor element is disposed, wherein
• the resistor element has:
• a titanium oxide containing region which is disposed on a side toward the center electrode and closest to the center electrode and contains titanium oxide;
• and
• a titanium oxide reduced region which is disposed on a side toward the metallic terminal member in relation to the titanium oxide containing region and whose titanium oxide content is lower than that of the titanium oxide containing region or which contains no titanium oxide, and
• as a whole, the titanium oxide content of the resistor element decreases from the center electrode side toward the metallic terminal member side.