To execute appropriately soldering to every object to be soldered, by recognizing the pattern of a temperature-time variation by measuring the temperature of a part to be heated, deciding whether a soldering state is good or not, and executing automatically a necessary step, based on the result of its decision. A laser oscillator 3 irradiates a laser power set in the beginning to a soldering part 20 and the temperature of the soldering part 20 is detected by a temperature sensor 7 and sent as information into a main control device 2. The device 2 measures a rise temperature during a minute time and decides whether the laser power is suitable or not, by deriving a temperature rise gradient. When the laser power is within a correct range, the main control device 2 calculates a control condition required for the control of a supply control device 6, and the control device 6 makes preparations for the feed operation or a solder supplying device 5, based on a control condition. From the laser power and the temperature rise gradient, the curve of an ideal temperature time variation is read out of an external memory 11, and the range of an allowable deviation is derived. When a measured temperature value is within an allowable error range in the measurement time, it is decided that soldering is normal. |