As the device passed the certification test that envisioned a factory environment, the wearer of it can perform a heavy work safely and tirelessly with simple operation. The device is safe as it is able to control its power so as not to exert a power to lift a heavy object which the wearer cannot lift without the assistance of the device. Brain signals which are sent to muscles leak on the skin surface as very faint signals, so called “bio-electric signals (BES). HAL reads BES and moves accordingly. In other words, HAL supports wearer’s motion by exactly moving in accordance with the wearer’s brain signals. In accordance with the variety of the work severity and the physical constitution of the wearer, the device’s assistance levels can be adjusted.