According to the Patent Law of the Republic of China, the period for granting invention patents is 20 years. This means that if an invention is protected by a patent, the inventor or his successor can enjoy the patent right within 20 years after the patent is granted. If the 20-year period expires, the invention will automatically enter the public domain and anyone can use it for free.
Note: The Patent Law of the Republic of China was promulgated on 1944 and may have been updated now. For the latest patent authorization period, I suggest you consult the latest version of the Patent Law of the Republic of China.