A road information vehicle mounted detection apparatus configured to acquire road information by emitting a beam via a transmission antenna having a variable directivity pattern from a measuring position to a road sign having a plurality of flat portions, each of the plurality of flat portions being one of a first flat portion in a direction normal to which the beam from the measuring position is incident and a second flat portion in a direction other than normal to which the beam from the measuring position is incident, the road information detection apparatus comprising: a transceiver circuit configured to control the transmission antenna to scan the beam by switching between a plurality of emission angles including a plurality of azimuth angles (θ1 - θn) relative to a front direction of the vehicle, and to receive, as reflected wave signals, reflected waves produced when the beam is reflected by the plurality of flat portions; a distance and reflected wave intensity detection unit configured to detect a plurality of distances (Ln) between the vehicle and the plurality of flat portions and a plurality of reflected wave intensities of the reflected waves reflected by the plurality of flat portions; an emission angle detection unit configured to detect the plurality of azimuth angles (θ1 - θn) of the reflected waves based on the reflected wave signals; and a road information analysis unit configured to acquire the road information corresponding to a plurality of bits of digital data by generating a heat map based on the plurality of azimuth angles (θ1 - θn), the plurality of distances (Ln), and the plurality of reflected wave intensities of the reflected waves, and analyzing the heat map by using a predetermined threshold value of the reflected wave intensity, the heat map being a mapping between the plurality of reflected wave intensities and the plurality of azimuth angles (θ1 - θn) and the plurality of distances (Ln), wherein the road information analysis unit is configured to generate each of the plurality of bits of digital data of a first value if a corresponding one of the plurality of reflected wave intensities is higher than or equal to the predetermined threshold value, and generates each of the plurality of bits of digital data of a second value if a corresponding one of the plurality of reflected wave intensities is lower than the predetermined threshold value. a transceiver circuit configured to control the transmission antenna to scan the beam by switching between a plurality of emission angles including a plurality of azimuth angles (θ1 - θn) relative to a front direction of the vehicle, and to receive, as reflected wave signals, reflected waves produced when the beam is reflected by the plurality of flat portions; a distance and reflected wave intensity detection unit configured to detect a plurality of distances (Ln) between the vehicle and the plurality of flat portions and a plurality of reflected wave intensities of the reflected waves reflected by the plurality of flat portions; an emission angle detection unit configured to detect the plurality of azimuth angles (θ1 - θn) of the reflected waves based on the reflected wave signals; and a road information analysis unit configured to acquire the road information corresponding to a plurality of bits of digital data by generating a heat map based on the plurality of azimuth angles (θ1 - θn), the plurality of distances (Ln), and the plurality of reflected wave intensities of the reflected waves, and analyzing the heat map by using a predetermined threshold value of the reflected wave intensity, the heat map being a mapping between the plurality of reflected wave intensities and the plurality of azimuth angles (θ1 - θn) and the plurality of distances (Ln), wherein the road information analysis unit is configured to generate each of the plurality of bits of digital data of a first value if a corresponding one of the plurality of reflected wave intensities is higher than or equal to the predetermined threshold value, and generates each of the plurality of bits of digital data of a second value if a corresponding one of the plurality of reflected wave intensities is lower than the predetermined threshold value.