In a configuration of a technique in the related art, since two Doppler sensors are used to measure velocity in two directions, and a set of transmission circuit and reception circuit are provided for each of directions to be measured, a device becomes large and expensive. Moreover, in the related art, since signal processing is performed by using output of each of the two Doppler sensors, axis adjustment in each of emission directions of the two Doppler sensors needs to be performed separately, therefore there is a difficulty that appropriate axis adjustment is complicated and difficult. An absolute velocity measuring device is mounted in a vehicle, and includes a transceiver for transmitting and receiving a wave, a transmission-wave branch section that branches a unidirectional wave transmitted from the transceiver in a plurality of directions, and converges reflected waves of waves branched in the plurality of directions from the ground into the unidirectional wave to be received by the transceiver, and a signal processing section that obtains a signal based on a reflected wave that has been received from the transceiver, and processes the obtained signal and thus calculates a plurality of kinds of behavioral information of the vehicle, and then outputs the relevant behavioral information.