Provided is an antenna device includes a base connector fixed to a support substrate, a module connector connected to the base connector to the base connector, and an antenna module fixed to the module connector and configured to transmit or receive a radio wave. The base connector includes a base-side casing, a base-side fitting portion, and multiple base-side terminals. The module connector includes a module-side casing, a module-side fitting portion, and a multiple module-side terminals. The antenna module includes an antenna substrate and an antenna element provided on a front surface of the antenna substrate. In a state in which the base connector is fixed to the support substrate and the module connector is connected to the base connector, the antenna module is fixed to the module-side casing such that the front surface of the antenna substrate faces up diagonally to the outside of the module connector.