Emperor Akihito will undergo surgery next month for prostate cancer, Japan's Imperial Household Agency announced Saturday.
Doctors examined Akihito, 69, Tuesday after blood tests over the past few years had shown "slightly worrisome" signs, an agency spokesman said.
A prostate biopsy revealed the cancer cells, the spokesman said.
Doctors believe that the cancer hasn't spread and that the emperor has a "good chance of a full recovery," he said.
The emperor is scheduled to undergo an operation at Tokyo University Hospital in mid-January to have the cancerous tissue removed and will be hospitalized for about a month, the spokesman said.
Akihito's eldest son, Crown Prince Naruhito, will temporarily assume the emperor's duties if necessary.
Agency officials said last week that the emperor had not had prostate problems in the past and had been feeling well.
But his annual January exam was moved up about a month after his recent blood tests in- dicated a possibility of pros- tate cancer, the spokesman said.
The emperor hadn't complained of pain or shown any other symptoms, he said.
The announcement will allow the emperor to withdraw from some New Year's festivities at the Imperial Palace, though he is still scheduled to appear for his traditional Jan. 1 holiday address.
Under Japan's postwar constitution, the royal family has no official political powers.