In case a robot performs work inside the box-shaped workpiece held on a jig 16, it is possible to avoid interference with an interference point 18 in a curved recessed space of the arm by curving the first arm of the robot 9 in a direction of rotation with respect to a swing part 4 and in a direction opposite to the interior angle formed by the first arm 9 and the second arm 12. This allows work to be done as far as the work bottom 19. As a result, it is possible to reserve a wider work area 20 inside the workpiece than the work area inside the workpiece of a related art robot.