Emperor Akihito remains in hospital in Toyko, where he is being treated for bronchitis.
The 77-year-old royal was admitted on November 6 as a precaution when he developed a fever.
He was originally supposed to be discharged last Friday, but after his temperature rose and his cough continued, it was decided to extend his stay.
The emperor missed the official visit of the king of Bhutan and his new queen this week.
This marks the first time he has missed a meeting with a state guest in more than two decades on the Chrysanthemum Throne.
It is the royal's second hospital stay this year after he was admitted in February for extensive tests to his arteries.
He has a history of stress-related illness, including irregular heartbeat and gastrointestinal problems.
For the moment, the emperor's son, Crown Prince Naruhito is fulfilling official duties on behalf of his father.
Photo: © Rex Features