To develop a mechanism that minimizes directional variation of pose accuracy, maximum operation speed, and maximum output force over a prescribed working space and minimizes required sensor resolution and maximum actuator power for generating required accuracy, speed, and force, we propose a global isotropy index as an evaluation index in mechanism design. The effectiveness of the global isotropy index was numerically confirmed through error analysis of output displacement and kinematic synthesis of spatial in-parallel actuated mechanisms with 6 degrees of freedom.