A cutting apparatus and opening method for a rectangular package covered with packaging material includes a platform for positioning a rectangular package. Spacing members are provided for forming a space between the packaging material and the packaged items on two mutually opposing planes of the package on the platform. A pair of cutting blades are mounted for cutting the packaging material from one edge to the other in the direction of height or width where a space is formed between the packaging material and the packaged items by the spacing members. A pair of cutting blades are also mounted for cutting the packaging material from one of the two edges other than the edges passing the starting point and the finishing point of each of the two cutting lines cut by the pair of cutting blades to the above-memtioned cutting lines. A second spacing member is provided for forming a space between the packaging material and the packaged items on the plane with two edges that pass the ends of the two cutting lines made by the pair of cutting blades. A cutting blade cuts the packaging material for connecting the two cutting lines on the above plane and a device is provided to open the packaging material from each area on the three planes provided with cutting lines.