Recently, development and research of surgical manipulator has been widely performed. In order to realize safer and more precise operation, force measurement and feedback are required. In this research, we have proposed a forceps manipulator which is able to estimate external force without force sensors using pneumatic cylinders. Furthermore, in this paper, we developed a pneumatic manipulator supporting forceps. The prototype manipulator has 3-DOFs which are driven by pneumatic cylinders. We estimated external forces acting on the tip of the manipulator measuring pressures of the cylinders and compared them with outputs of a force sensor. Experimental results showed that the developed system successfully estimated the external force in x,y component.