PURPOSE: To execute a heating treatment of solder in good condition and to surely stick electronic parts to an electrode part on a substrate by cooling a soaking zone with a cooling means and restraining the excess raising of the temp. in the soaking zone.

CONSTITUTION: The substrate 8 mounting the electronic parts 7 by a tip mount is conveyed in a heating chamber 1 with a conveyor 6 to execute the heating treatment of the solder sticking the electronic parts 7 to the substrate 8. Therein, as the soaking zone T2 is cooled by a cooling pipe 14, the excess raising of the temp. caused by conduction of the heat from a preheating zone T1 and a reflow zone T3 is restrained, and the ideal temp. profile is obtd. and the solder is ideally heated and melted, and the electronic parts 7 can firmly be stuck to the electrode part on the substrate 8.