An electronic circuit device that suppresses deformation of an adhesive layer of a flexible printed circuit board during formation of a resin seal portion, and suppresses deterioration of the circuit board caused by deformation of the adhesive layer. The electronic circuit device includes a substrate mounted with an electronic component; a flexible printed circuit board electrically connectable to the substrate and an external device, and includes a wiring conductor and a pair of insulation films covering upper and lower surfaces of the wiring conductor; and a resin molding portion to seal the substrate and a portion of the circuit board. The wiring conductor of the circuit board is adhered through an adhesive layer to at least one of the pair of insulation films, and a dummy wiring material that does not function as wiring is disposed on an outer side of a border between the circuit board and an outer peripheral portion of the plastic molding portion, and disposed between the pair of insulation films.