PURPOSE: To equally heat the whole of a substrate and to perform sure soldering by equalizing the deviation of heat capacity between different sections by arrangement of a heat capacity regulation member.

CONSTITUTION: The mounting surface of the substrate 1 to mount plural kinds of circuit parts 3 is divided into plural sections 4 based on the size of heat capacity in consideration of heat capacity peculiar to each circuit part 3 and the occupation area on the substrate 1. By this method, the sections 4 assumed virtually are also ranges where solder 2 shows the almost same behavior with respect to heating in a reflow furnace and the deviation of heat capacity between the different sections 4 is equalized by arrangement of the heat capacity regulation member 5, by which heat capacity is equalized extending over the entire surface of the substrate 1. Accordingly, since the whole solder 2 starts to melt at the almost same time in the reflow furnace, various failures such as drooping-down of the solder are prevented surely.