Noise emitted from a copy machine during operation involves periodic impact sounds generated from the printing process, such as those of rollers picking up and releasing paper. To investigate the effect of the temporal structure of operating sounds on the sound quality of copy machine noise, psychoacoustical experiments were carried out using synthesized stimuli in which the timings of three kinds of generated impact sounds were systematically controlled within a cycle of paper output (1000-3000 ms). Results revealed that stimuli with shorter paper output cycles were rated as more pleasant. Furthermore, the impact sound generated when a sheet of paper is correctly positioned before being put into a photoconductor drum by a roller (resist roller) significantly affected auditory pleasantness. In particular, the timing of this impact resist roller sound (RR sound) generated within a paper output cycle was found to be important. Stimuli in which an RR sound was generated at 300- 500 ms after the start of periodic operating sounds were evaluated as most pleasant. Considering the temporal centroid of the RR sound waveform, the timing of the abovementioned RR sound was determined to be approximately 400-600 ms. This timing is similar to the interval of repeated sounds or lights most favored and felt as most natural by humans. The ratings of agreeableness for the timing of RR sounds obtained in the present study are concluded as being related to the interval most favored by humans.