A method and device capable of properly selecting light radiating conditions in soldering work where components are soldered onto a board with light radiation applied to a solder joint. The device for selecting the light radiation conditions may contain a) an input device for entering information on; b) a storage for storing at least any one of databases on light radiation power and light radiation time for soldering; c) a calculator for determining light radiating conditions according to the information entered through the input device and the database stored in the storage; and d) an output device for outputting the light radiating conditions determined by the calculator. The input device may further comprise i) a component; ii) a board on which the component is soldered; and iii) solder for soldering the component.