The subject innovation relates to a underbody protection, the elastic supporting by a spring in the internal bumper is provided on the driving gear which vertically drives and the sense plate formed so as to be up and down, rotates the sensing plate, the inner upper end of the bumper the sensing plate When the contact with the proximity switch for all of the components and a locking switch for outputting the locking signal for not operating, when the detected plate-up in the on-state outputs a predetermined electric signal, which allows the detection plate user to the up-down up-down switch and the locking switch and a control unit for controlling the respective components in accordance with the operation of the up-down switch, the underbody of the vehicle and wherein the-part alarm sound generator for generating a warning sound where the predetermined electric signal is inputted from the proximity switch is It relates to an underbody protection device for protection from the projections.