The health ministry said 19 new infections have been confirmed since last week.
All are believed to have visited Tokyo's Yoyogi Park or its environs, one of the major green lungs of the metropolis, popular with residents and tourists alike.
The park, one of the largest open spaces in central Tokyo, is believed to be the source of the mosquito-borne disease.
The first three sufferers, who were found to be infected last week, had also visited the park, where Tokyo officials have now sprayed about 800 litres (210 US gallons) of pesticide in a bid to kill off the insect colony.
The last domestic infection of dengue fever was in 1945, although there are around 200 cases annually among Japanese who have travelled abroad, mainly in Southeast Asia.
Dengue fever is not transmitted directly from person- to- person and symptoms range from mild fever to incapacitating high temperatures, according to the World Health Organisation.
There is no vaccine or any specific medicine to treat dengue and patients should rest, drink plenty of fluids and reduce the fever using paracetamol, it says.
Meanwhile, shares in home pesticide maker Fumakilla were up 22.85 per cent at 430 yen on the Tokyo Stock Exchange. That follows a nearly 25 per cent rise one day last week.
