this invention provides a ground - speed measuring apparatus for a vehicle that can detect a velocity along the movement of the vehicle , a velocity across the movement of the vehicle , a side - skid angle of the vehicle , and an angular velocity of the vehicle . a ground - speed measuring apparatus comprising three or more transceivers each of which contains a transmitter for transmitting a wave and a receiver for receiving a reflection of the wave transmitted from the transmitter , wherein at least three of said transceivers are placed outside a cylindrical area whose axis of symmetry passes through a point on the floor of the vehicle , three straight lines which respectively pass through said transceivers perpendicularly thereto intersect with each other or skewed in said cylindrical area , and the transmitter of each transceiver is at a preset angle with the floor of the vehicle .