Since a patent right is also a kind of property right, an act of infringement of a patent right constitutes a tort, and a patentee who sustains damages as a result of an act of infringement may demand damages from the infringer in tort (Article 709 of the Civil Code). Unlike an ordinary tortious act however, in the case of the infringement of a patent right, it is often difficult to prove the amount of the loss, as well as intent or negligence on the part of the infringer. For that reason, the Patent Act contains a special provision for calculating the amount of loss (Article 102), a provision on the presumption of negligence (Article 103), and a provision permitting the determination of a reasonable amount of loss (Article 105-3).