The purpose of the present invention is to provide a workpiece bonding method by which three workpieces can be efficiently bonded together while obtaining an expected bonding state without causing an increase in the complexity or size of the apparatus structure, and a light irradiation apparatus used in the bonding method. The workpiece bonding method according to the present invention is a method for bonding a second workpiece and a third workpiece to both surfaces of a first workpiece, the first workpiece being made from an ultraviolet transmitting material, and the method comprising: an ultraviolet irradiation step of irradiating bonding surfaces of the respective workpieces with ultraviolet light; and a bonding step of laminating and bonding the respective workpieces together such that the respective bonding surfaces irradiated with the ultraviolet light adhere closely to each other. The ultraviolet irradiation step for the first workpiece is performed with the respective bonding surfaces of the first wor
