A robot apparatus includes a base, a strut unit, and a linear expansion mechanism 1 rotatably supported on the strut unit. The linear expansion mechanism includes: a plurality of cylindrical bodies assembled in series to each other; a block train including a plurality of blocks coupled to each other in a row, the block at the leading end being connected to the cylindrical body at the leading end; and a housing part that houses the block train along an arc-shaped trajectory, the housing part being arranged below the cylindrical body at the trailing end and above the strut unit.