PURPOSE: To perform soldering of multiple spots in a short time, by laying a heat resistant plate holding solders in corresponding soldering spots on a wiring circuit board having multiple soldering spots, and fusing the solders by heating from the surface of the heat resistant plate.

CONSTITUTION: A soldering heat resistant plate 3 is laid over a machine part 1 comprising a wiring circuit having multiple soldering spots 2. The soldering heat resistant plate 3 is a 2W3mm thick plate having heat resistant fiber material and flexibility of resin material, and has pierced parts or recess parts 6 in the corresponding soldering positions of the part 1, which are filled with flux and solders 7. In order that the solders 7 may not drop off the heat resistant plate 3, a film 9 of a lower melting point that the solder is adhered thereto. This plate is laid over the wiring circuit board 8 of the part 1 and pressurized, and heated with heat gas or the like from the surface of the heat resistant plate 3. As a result, the solders in the recess parts 6 melt, so that the soldering spots 2 of the wiring circuit of the part 1 may be soldered simultaneously.