A user operating a mechanical devise receives sensory information (e.g., sounds and vibrations) generated by the mechanical operation in response to the operation input. With the digitization of products, the mechanical operation response is removed as is the associated sensory information, thus there is no confirmation of the completed operation. Adding a digital sound or vibration could solve this problem. The challenge, however, is designing an operation response without inducing any sense of discrepancy. The purpose of this study was to create a quantitative, objective method to evaluate the sense of discrepancy to the operation response and the habituation to the response. We investigated the possibility of using an event-related potential component (P300), believed to reflect attention to stimuli, as a quantitative evaluation method of the sense of discrepancy. Experiment 1: We studied the sense of discrepancy between the type of operation response (sound, vibration, none), and the shutter operation of a mirrorless single-lens camera, using subjective evaluation and the P300. We confirmed that the P300 amplitude corresponded to the degree of the sense of discrepancy. Experiment 2: With the mouse click being the operation sound, the attenuation of the P300 amplitude by the repeated operation was consistent with the subjective habituation to the response. We conclude, based on these results, that the P300 amplitude could help determine the sense of discrepancy to the operation response and the habituation to the response.