A self-rating instrument for measuring continuous and real-time affect states was developed. In Experiment 1, using an edited film that was switched from a positive mood video to a negative mood video, the validity of this method for rating participants' subjective emotionality was examined. In Experiment 2, in one condition the participants evaluated their affects in real time, and in the other condition they did not. Differences in the participants' affects in the two conditions were estimated. Results indicated that this rating method could evaluate affects continuously and validly. Moreover, the method did not interfere with the affects that were being measured.