An antenna device comprising: a shielded cable having a first connection portion on one end side and a second connection portion on the other end side; and an antenna element which is connected to a first outer conductor of the shielded cable at the second connection portion of the shielded cable, wherein the shielded cable includes an inner conductor, a first insulator, the first outer conductor, a second insulator, and a second outer conductor, which are coaxially disposed in this order from an inner side, and is covered at its outer circumference by an insulation sheath, the first connection portion of the shielded cable is formed such that the inner conductor is configured to be supplied with power and the first outer conductor is connectable to a ground, and in the second connection portion of the shielded cable, the inner conductor is connected to the second outer conductor; wherein the first outer conductor is formed by a braided shield which is braided by a plurality of element wires having an electrically-conductive property; characterised in that: a coupling state of the second insulator and the first outer conductor is coarser than a coupling state of the second insulator and the second outer conductor; the second insulator is formed of polyethylene and is formed by an extrusion molding process carried out at a temperature greater than the melting point of the polyethylene; and a seal film is disposed between the second insulator and the first outer conductor to prevent melted polyethylene resin to soak into the interwoven portion of the braided shield. a shielded cable having a first connection portion on one end side and a second connection portion on the other end side; and an antenna element which is connected to a first outer conductor of the shielded cable at the second connection portion of the shielded cable, wherein the shielded cable includes an inner conductor, a first insulator, the first outer conductor, a second insulator, and a second outer conductor, which are coaxially disposed in this order from an inner side, and is covered at its outer circumference by an insulation sheath, the first connection portion of the shielded cable is formed such that the inner conductor is configured to be supplied with power and the first outer conductor is connectable to a ground, and in the second connection portion of the shielded cable, the inner conductor is connected to the second outer conductor; wherein the first outer conductor is formed by a braided shield which is braided by a plurality of element wires having an electrically-conductive property; characterised in that: a coupling state of the second insulator and the first outer conductor is coarser than a coupling state of the second insulator and the second outer conductor; the second insulator is formed of polyethylene and is formed by an extrusion molding process carried out at a temperature greater than the melting point of the polyethylene; and a seal film is disposed between the second insulator and the first outer conductor to prevent melted polyethylene resin to soak into the interwoven portion of the braided shield. a coupling state of the second insulator and the first outer conductor is coarser than a coupling state of the second insulator and the second outer conductor; the second insulator is formed of polyethylene and is formed by an extrusion molding process carried out at a temperature greater than the melting point of the polyethylene; and a seal film is disposed between the second insulator and the first outer conductor to prevent melted polyethylene resin to soak into the interwoven portion of the braided shield.