In this research, a flat-type pneumatic actuator aimed to be applied to mobile robots working in narrow spaces or wearable devices has been developed. The actuator is configured with small diameter McKibben Artificial Muscles which show high flexibility and generate contraction force in axial direction. By integrating the artificial muscles parallelly, the actuator can contract in the longitudinal direction and bend in any direction by changing the applied air pressure pattern to the artificial muscles. In this paper, structure of the actuator is proposed and the fabrication process is established. The developed prototype actuator is configured with three artificial muscles of length 50[mm], width 5[mm] and thickness 2.6[mm]. The bending motion with the minimum radius of curvature of 21.3[mm] and contraction motion with the maximum displacement of 9.3 [mm] in the longitudinal direction are performed.