Considering effects of manufacturing tolerance on a performance, a robust design optimization using a surrogate model is applied for an electrical machine. When constructing the surrogate model for the robust design, it can be required to reduce the number of design variables because of the high computational costs. Therefore, a sensitivity analysis method for robust performance which is affected by manufacturing tolerance is investigated in this paper. Analysis of variance (ANOVA) is employed for the sensitivity analysis. An orthogonal array using a combination of inner and outer array is used for the ANOVA. The proposed method was applied to an interior permanent magnet synchronous motor and the results were verified with a Monte Carlo simulation.