Provided is a vehicle-mounted radar device capable of obtaining a high azimuth resolution with a simple configuration.The vehicle-mounted radar device is mounted on a vehicle, and includes: a detector for irradiating a periphery of the vehicle with electromagnetic waves, and for outputting a reception signal obtained from reflected waves that are reflected from an object that exists in the periphery of the vehicle; a vehicle information calculator for calculating information related to a movement of the vehicle with a use of vehicle information of the vehicle; a storage unit for storing a plurality of the reception signals outputted by the detector at different time points; and a synthetic aperture processor for conducting a synthetic aperture processing on the reception signals obtained by the vehicle at different positions, based on the information related to the movement of the vehicle.