The bending mechanism of a conventional endoscope operates by drawing wires from outside the human body. The shaft structure of endoscopes is relatively complex to avoid buckling caused by wire traction. In this study, one directional bending mechanisms using shape memory alloy (SMA) wires have been developed for minimally invasive medicine. A large bending angle was accomplished by positioning a working point of driven SMA wires near a center point of the mechanism and by surrounding the SMA wires and an inner tube by helical thin metal wire. External diameter and length of the bending part of the mechanism are 4.1 mm and 35 mm respectively. The curvature radius of the fabricated device is 20 mm while maintaining the surface temperature of the device under 41°C in environmental temperature (38°C). Servo control has been considered to be suitable for the application of active bending mechanisms as micro robots. Feedback control by changing in the electrical resistance of the SMA wire was utilized for precise and safty actuation.