A device to safeguard a horse in a horse carrier or trailer includes a harness (25,26) on the horse and the safety belts (28-31) affixed to the walls of the carrier (14-16) at the level of the breast of the horse. The harness is fastened around the breast and secured around the withers and ribcage so that its connecting device (44) is situated at the level of the breast of the horse. The horse is lead into the trailer or carrier and preferably tethered, before, standing in front of the horse, one affixes the harness to the safety belts.