Emperor Hirohito's prolonged illness has momentarily derailed the booming Japanese economy, sending stock prices down and curtailing advertising and retail business, company officials said Thursday.

"The emperor's illness is, without doubt, the major factor depressing the market these days," said a representative of Nomura Securities Co., Japan's top brokerage house.The key indicator on the Tokyo Stock Exchange, the Nikkei average, has fallen 728.66 yen since the frail Hirohito, 87, became seriously ill Sept. 19.

Hirohito remained in serious but stable condition Thursday, and the stock market fell for the fifth straight session, closing at 27,172.34 yen, down 233.15 yen from Wednesday.

The emperor's illness has also cut into advertising and department store business.

Advertisers have canceled ad campaigns and department stores have postponed new promotions due to a Japanese custom that shuns flashy displays during a period of mourning.

"We are concerned how long this situation will continue because it is causing people in our business to worry," said an official of Dentsu Ltd., the world's top advertising agency.