A circuit board device of the embodiment includes: a mount board (10) having an electronic component (12) and a printed circuit board (11) having at least one surface where the electronic component is mounted; a heat path (40) arranged to a position facing the mount surface of the mount board, a sheet (30) arranged on the mount surface, and a resin portion (20) arranged between the sheet and the heat path. A cavity (D) surrounded by the sheet and the mount surface is formed in a step portion between the electronic component and the printed circuit board.