A vehicle-mounted antenna device includes an antenna, an electronic component, a coaxial cable and a shielding member. The electronic component is electrically isolated from the antenna. The electronic component has a coaxial connector including an inner terminal and an outer terminal. The coaxial cable has one end connected to the coaxial connector. The shielding member is grounded to a vehicle body being ground. The shielding member is configured to block at least part of noise generated from the electronic component from reaching the antenna. The coaxial cable includes an inner conductor connected to the inner terminal and an outer conductor connected to the outer terminal. The electronic component is electrically connected to the shielding member via only the outer terminal.