Recently, commercially available computer-aided surgical robot systems have been introduced to enable surgeons to improve the accuracy of cutting and alignment in total knee arthroplasty (TKA). The minimal invasive surgery (MIS) in the TKA has been increased since MIS can improve the surgical outcomes such as the recovery time and hospital stay by reducing the incision in surgery. However, current surgical robot systems do not provide the MIS TKA capability. In this study, we developed a laboratory-level surgical robot system to cut the bone from the lateral direction of the knee joint to provide MIS TKA. TKA experiments with saw bones of femur were compared between the conventional approach and the MIS approach. The incision length for the working space of the cutting tool and bone cutting time were decreased in lateral direction bone cutting. In addition, the cutting surface was smoother and the ranges of motion of all six joints were decreased in lateral direction bone cutting. Moreover, the cutting accuracy in terms of the lengths and angles of five cutting planes in femur were smaller in lateral approach than those in conventional approach. Therefore, consideration of bone cutting from the lateral direction in robotic TKA surgery should be necessary to improve the surgical outcomes in knee arthroplasty. The developed surgical robot system could be a platform of various orthopedic robotic surgeries.