Traditionally, parameter design based on quality engineering and securing a high level of robustness have been necessary in the design of measuring apparatus. In parameter design, the level values for control factors can be expressed through point values. An optimal condition is selected from among the defined level values when combining the control factors with a high signal-to-noise (SN) ratio. However, to perform additional searches for conditions adjacent to the level values, additional tests using nontraditional experiment conditions are necessary. This paper proposes a robust design method for searching outside level values of design parameter by expressing the control factors as a range of values rather than point values. The proposed design method evaluates a range solution for conditions with a high SN ratio by introducing evaluation indicators that take into consideration the intent of the designer. This study derives the range solution with optimal conditions estimated in conventional parameter design by applying the proposed method to the design of a T-peel test apparatus for delamination. The results confirmed that using the proposed method, an outside level value for high SN ratio range solution defined in the parameter design can be derived.