A spark plug includes a tubular metallic shell having an attachment screw portion having an external thread. The attachment screw portion has a pitch diameter maximum portion at which the external thread has a maximum pitch diameter, the pitch diameter maximum portion being located on a rear end side of a center of the attachment screw portion in a direction along an axial line of the metallic shell, and a pitch diameter local maximum portion at which the external thread has a locally maximum pitch diameter, the pitch diameter local maximum portion being located on a forward end side of the pitch diameter maximum portion in the direction along the axial line.