A folding device having a rectangular bottom transports an animal such as a dog.In the unfolded state, upright first and second side walls are connected on the long sides and short sides of the bottom.Fold lines in the second side walls facilitate folding of the device from the unfolded state to the folded state and the bottom is divided into bottom portions by a fold line running parallel with the long sides to facilitate folding the device from the unfolded state to the folded state. Rigidity-providing wall portions are provided at the location of at least one of the corners, which stiffness-providing wall portions can be secured to the second side walls, which stiffness-providing wall portions are hingable about an axis transverse to the rectangular bottom at the location of the relevant corner for increasing the stiffness of the second side walls.