A method of manufacturing a spark plug includes a step (a) of chucking, by mutually facing chucks, a metallic shell (50) extending along its center axis (O-O) so as to fix the metallic shell (50), and (b) a step of pressing a ground electrode (30) against the fixed metallic shell (50) and applying voltage between the ground electrode and the chucks for resistance-welding the ground electrode and the metallic shell. A first chuck (210) facing a second chuck (220), wherein, as viewed on an imaginary plane of projection perpendicular to the center axis, the number of support points (sp3) on the second chuck (200) is smaller than the number of support points (sp1, sp2) on the first chuck (210) for supporting the metallic shell (50).