Laser welding method and laser welding device

A laser welding device that joins a first member in the shape of a plate and made of a metal material to a second member made of a metal material by laser welding, the laser welding device comprising:

• a laser oscillator that generates a laser beam;
• a light-condensing unit that condenses the laser beam;
• a scanning unit that scans the laser beam to form a spot;
• and
• a control unit that controls the laser oscillator and the scanning unit,
• wherein the control unit allows the other main surface of the first member to be irradiated with the laser beam, the other main surface being a main surface opposite to the one main surface of the first member which the second member is brought into contact with or brought close to, in a state in which the second member is brought into contact with or brought close to one main surface of the first member,
• whereby the irradiation of the laser beam melts the first member and the second member to form a weld portion having a substantially circular or oval shape in a plan view and form a fillet on a joined portion between the first member and the second member.