This paper is using practical case study of robust design engineering. Effect of control factors and optimum condition is studied to design a more robust Paper Permeability Tester. In this study, robustness means decreasing uncertainty that is validity of measurement results with the Tester. Robustness is required to ensure the reliability for the measurement results in the field of the measurement tester. Thus, orthogonal array L18 is employed and the optimum condition was obtained for decreasing the measurement dispersion. Experiment reproducibility of Signal-to-Noise Ratio and sensitivity were confirmed within 20%. SNR value is linearly depends on air permeance value. When the value of air permeance is small, it tends to provide small SNR. Flow rate in nozzle was considered as a major cause. Stability of flow in the nozzle is significant to design the Tester to be more robustness. In a case of a flow under the rapidly, SNR is small due unstable flow. Sensitivity with nozzle diameter was dramatically large. Nozzle specification tolerance was found to have strong influence on measurement result.