For the ECU that controls an electronic fuel injection system, we applied a card edge connector, which is a consumer electronics technol., and the transfer molding technol. generally using a semiconductor manufacturing method.In the developed ECU, and the entire printed circuit board except the edge connector terminals was sealed with a specialized epoxy resin.This was the practical use of the world's first waterproof structure in the ECU alone.In addition, we have developed a waterproof card edge connector that mates with this ECU.A new insertion mechanism, multiple contact terminals, and the printed circuit board with little strength change were used, satisfying the durability requirements for motorcycles.These technologies, applied to the ECU, have achieved more than five times the productivity and 20% cost reduction compared to the conventional type.The developed product has been put into practical use for small motorcycles since the 2018 model.