Global demand for portable digital music players is expected to nearly quadruple to 104 million units a year by 2009.

The increment is fueled by falling prices, better equipment and a greater availability of legal music, according to a study released on Tuesday.

Led by consumer excitement for Apple Computer Inc. iPod music players, demand for both hard disk drive and Flash memory-based portable audio devices -- also called MP3 players -- is seen jumping from 27.8 million units in 2004, according to research firm In-Stat.

In-Stat said revenue for both hard disk and Flash-based MP3 players reached about $4.5 billion, an increase of almost 200 percent over 2003.

Apple holds a 30.2 percent share of the worldwide portable audio players market, In-Stat said. Other leading vendors include D&M Holdings Inc.'s Rio, South Korea's Reigncom Ltd's iRiver and Creative Technology Ltd.'s Creative Zen line.