PURPOSE: To provide a legless chair by which width adjusting motion is easily performed, and load marks and a scratch are prevented from being generated on a tatami (rush mat in japanese domestic life) or a floor by always holding a supporting state by a load supporting part simultaneously, and high stability is attained when a person sits while receiving assistance for a sitting operation and a standing operation, as well as a simple mechanism and a reduced manufacturing cost.

CONSTITUTION: This device is provided with a main body chassis 14 on which a chair is installed, the load supporting part 16 mounted on the main body chassis 14, and a rolling wheel supporting part 20 arranged below the chassis 14 and equipped with a rolling wheel 18 on the lower face side, and a first pneumatic elevation part which moves the main body chassis 14 in a vertical direction with air pressure is provided between the main body chassis 14 and the rolling wheel supporting part 20, and whole load supporting states supported by the load supporting part 16 and that by the rolling wheel are selectively held correspondingly to the ascending/descending operation of the first pneumatic elevation part.