To automatically connect a rigid substrate and a flexible substrate electrically and mechanically by using solder-coated pins and then dipping the substrates in a solder bath.

A flexible substrate 32 and a rigid substrate 31, each having pin insertion holes 320, 310 at specified places, are laid on top of each other with the pin insertion holes 320, 310 being aligned with each other. Then, pins 33 with flanges preliminarily coated with solder 34 are inserted, from the flexible substrate 32 side, into the pin insertion holes 320 and then 310. After that, the lower face of the rigid substrate 31 is dipped in a solder bath to connect the two substrates 31, 32. By this method, the rigid substrate 31 and the flexible substrate 32 can be easily and surely connected.