This study aimed to confirm that people with high levels of over-adaptive tendencies have a response bias in that they respond to over-adaptation scales at a lower level than their actual tendencies. A survey was conducted on 279 undergraduate students, who responded to both the Over-Adaptation Scale (Ishizu & Anbo, 2008) and Over-Adaptive Behaviors Threatening Mental Health Scale (hereinafter called “the behavioral scale”). For the latter, in addition to their own evaluations, the participants responded with their inferences of evaluations by others. Participants were asked to assume that the other person was ‟the one who knew them the best.” Since people with high levels of over-adaptive tendencies are resistant to responding as if someone important to them did not understand them, inferring the evaluations by others was expected to reduce their response bias. We examined the relationship between their responses comprising self-evaluations and their inferences of evaluations by others. We found that the inference of evaluation by others on the “behavioral scale,” which is unaffected by bias, showed an upward convex curvilinear relationship to the Over-Adaptation Scale (Ishizu & Anbo, 2008), which is affected by bias. This result suggests the presence of a response bias.