In this paper, we propose 3 degree-of-freedom dual-arm microrobot called Robotic-Investigator (RI) which enables manipulation and force sensing for microorganisms in a microfluidic chip. The untethered RI is actuated by permanent magnets. Therefore, the RI can supply mN order force to stimulate microorganisms with measuring the applied force. To develop the untethered RI with force sensing structure, the layered fabrication technique and on-chip separation mechanism are introduced. Through the basic experiment, we confirmed that the untethered RI with thin structure was developed by proposed fabrication methods without any damage to RI. We also perform the manipulation and force sensing experiment for microorganisms in a microfluidic chip by the developed RI.