Cyberdyne said its 22 pound (10 kilogram) HAL _ short for hybrid assistive limb _ is equipped with sensors that read brain signals directing limb movement through the skin.

Wearing HAL, the three people took an hour-long train ride Monday from Tsukuba, north of the Japanese capital, to downtown Tokyo.

"HAL is to help people with weak leg muscles and mobility problems ... We wanted to show HAL is very useful for our daily life," said company official Takatoshi Kuno.

Belted to the waist, HAL relays brain signals to mechanical leg braces strapped to the thighs and knees, which then provide robotic assistance to people with weak limbs.

HAL comes in three sizes _ small, medium and large _ and has a one-leg version for a 150,000 yen ($1,570) monthly rental fee, while a two-leg unit goes for 220,000 yen ($2,300) a month. It was unclear when HAL would go on sale to the public or what the price tag will be.

The robotics company declined to say how much it cost to manufacture HAL.

Cyberdyne said the United States and some European nations have expressed interest, but it did not elaborate further.

HAL may have far-reaching benefits for the disabled and elderly. Japan is grappling with a rapidly aging society. About one-fifth of the population of 128 million is 65 or older, and that figure is expected to double in the next 30 years.