Method of detecting center coordinates of spot welding mark, laser welding method, and bonding method

A method of detecting center coordinates of a spot welding mark, the method comprising:

• a linear laser light emitting step of emitting a plurality of linear laser light components with a linear irradiation trace on a spot welding mark by emitting laser light through continuous output oscillation in a laser welding device in at least one of a direction from inside to outside of the spot welding mark and a direction from outside to inside of the spot welding mark;
• a waveform acquiring step of acquiring a waveform of an intensity of return light which is light generated from a processing point by emitting the laser light in the linear laser light emitting step;
• an outer edge position coordinates deriving step of deriving position coordinates of three or more points on an outer edge of the spot welding mark from a peak position of the intensity of the waveform of the return light;
• and
• a center coordinates calculating step of calculating center coordinates of the spot welding mark from the position coordinates of the three or more points on the outer edge derived in the outer edge position coordinates deriving step.