In this study, the verification of the questionnaire for the level of mental model building was examined from viewpoint of the actual users' operation. The user testing is conducted to grasp the level of mental model building. The validity of the questionnaire was investigated in terms of (a) operation time of the digital camera, (b) operation errors of the digital camera and (c) Structural model / Functional mode (the test result for measurement the level of mental model building after the operation). Then, the correlation between the score of the user testing and the questionnaire score was calculated. As the result, the significant correlation is confirmed between each score and the questionnaire score. Then, we believed the proposed questionnaire can be measured the users' mental model building level in the user-interfaces operation.