An octopus arm has no rigid structure, it is mostly composed of muscles aligned in various directions and the nerves. The muscles are roughly aligned in three directions, and by driving the muscles selectively, the octopus arm can perform multiple functions such as the contracting, bending, torsion and stiffness alteration. This study aims at the development of a new flexible robotic arm using thin McKibben actuators mimicking the muscle structure of an octopus arm. The McKibben actuator is a well-known pneumatic artificial muscle, and we have developed extremely thin McKibben actuators by using a braiding machine. In this paper, configuration of the flexible arm is proposed. The developed mechanism consists of thirty two thin McKibben actuators arranged in three directions, axial, radial and oblique, imitating the muscle structure of an actual octopus arm. The fundamental motion of the flexible arm is investigated experimentally. The proposed mechanism performs bending, contracting, torsion movements and stiffness alteration like an octopus arm.