A method of determining a laser welding condition, the method comprising: a first step of receiving an input of workpiece information indicating characteristics of a workpiece, the workpiece information including material, a board thickness, and a joint shape of the workpiece; a second step of receiving an input of laser information indicating characteristics of laser light; characterized by a third step of calculating a plurality of welding conditions consisting of a recommended laser power of the laser light, a recommended welding speed, a recommended welding pattern, an estimated strength of a welded portion, and an estimated weld depth of the welded portion based on an arithmetic equation or a database which associates the workpiece information and the laser information with the plurality of welding conditions, and displaying the calculated welding conditions; a fourth step in which an operator changes the recommended laser power of the laser light and the recommended welding speed, displayed by the third step, and a fifth step of recalculating based on the arithmetic equation or the database, in accordance with the changed laser power of the laser light and the changed welding speed, the recommended welding pattern, the estimated strength of a welded portion, and the estimated weld depth of the welded portion, and displaying the changed laser power of the laser light, the changed welding speed, the recalculated recommended welding pattern, the recalculated estimated strength of the welded portion, and the recalculated estimated weld depth of the welded portion, wherein the fourth step and the fifth step are repeated two or more times. a first step of receiving an input of workpiece information indicating characteristics of a workpiece, the workpiece information including material, a board thickness, and a joint shape of the workpiece; a second step of receiving an input of laser information indicating characteristics of laser light; characterized by a third step of calculating a plurality of welding conditions consisting of a recommended laser power of the laser light, a recommended welding speed, a recommended welding pattern, an estimated strength of a welded portion, and an estimated weld depth of the welded portion based on an arithmetic equation or a database which associates the workpiece information and the laser information with the plurality of welding conditions, and displaying the calculated welding conditions; a fourth step in which an operator changes the recommended laser power of the laser light and the recommended welding speed, displayed by the third step, and a fifth step of recalculating based on the arithmetic equation or the database, in accordance with the changed laser power of the laser light and the changed welding speed, the recommended welding pattern, the estimated strength of a welded portion, and the estimated weld depth of the welded portion, and displaying the changed laser power of the laser light, the changed welding speed, the recalculated recommended welding pattern, the recalculated estimated strength of the welded portion, and the recalculated estimated weld depth of the welded portion, wherein the fourth step and the fifth step are repeated two or more times. <EOS>