1. A vehicle-mounted antenna device having an antenna mast, the vehicle-mounted antenna device comprising:
a base plate on which a circuit board is placed;
a housing covering the base plate;
an antenna mast base structure, on which the antenna mast is provided, fitted to the housing; and
a water discharge flow path linearly formed in the housing as viewed from the upper portion of the vehicle-mounted antenna device, which extends continuously underneath the antenna mast base structure while being inclined relative to the base plate.