A thin board-to-board connector with high density in which there is no connection between three-dimensional complex metal springs. The board-to-board connector includes a connector having a bump for electrical connection having an umbrella shape on a board and connected to a circuit board and a connector having an elastic electrically conductive section having a through hole made in a conductive pattern on an elastic insulating board and connected to a circuit board electrically connected to the elastic conductive section. When a bump is inserted into the through hole, the elastic conductive section is electrically connected to the bump, and the side surface of the through hole is pressed against to the bump and elastically deformed and dented. Consequently, the bump is press-fit into the through hole. With this, the bump can be inserted into the elastic conductive section and engaged with it, and thereby electrical and mechanical connection between circuit boards can be simultaneously achieved in a two-dimensional manner, realizing a low-height connector.