The cells in living tissue change not only their proliferation and motility, but also their mechanical properties in response to external mechanical stimuli. The mechanical properties of the cells and their adhesion strength with the extracellular matrix are extremely important for understanding cellular mechanotransduction mechanism and in regenerating of load-bearing biological tissues such as blood vessels, bones, and ligaments. On these backgrounds, a micro tensile tester for investigating the mechanical properties of isolated cells was developed in our laboratory. However, the tester required many manual operations for force-deformation analysis resulting a large time consumption. Therefore, in this study, we developed a micro-tensile tester capable of in situ measurement of force applied to the cells and their deformation by using image-based real-time analysis for the deflection of a glass micro needle attached to the specimen cells. Using this tester, we measured the tensile stiffness of cervical cancer HeLa cells and their adhesion strength to the substrate. We found that the tensile stiffness and adhesion strength of HeLa cells were approximately 1/4–1/5 of the reported values of vascular smooth muscle cells, indicating the structural differences in the both types of cells. This finding strongly indicates that the whole cell mechanical properties, adhesion forces, and intracellular structures in cancer cells are deeply involved in their physiological functions, including migration in a narrow space and further division and proliferative ability.