Article 30 of the Japanese Patent Law defines “Exceptions to lack of novelty of invention”.
Under the current Japanese patent law, there is a 6 months grace period for an invention that has lost its novelty against the will of the inventor or due to the inventor’s own act.
However, the Japanese patent law has been revised, and the new grace period is 1 year. The new law applies to Japanese patent applications filed on or after June 6, 2018.