Difficulty in falling asleep has become a problem in Japan. However, quantitative effects on sleep quality have not been shown. In this study, we developed a system to induce sleep onset using Heart Rate (HR) feedback and examined the reduction of sleep latency by extending the heartbeat interval using the retraction phenomenon. Six males (22.5±1.0 years old) took a nap for 30 minutes for two times, without and with a sound, which has a lower tempo than the current HR. Electroencephalogram (EEG) was used to evaluate the shortening of sleep latency, and Electrocardiogram (ECG) was used to evaluate the changes in HR and Parasympathetic Nervous System (PNS). As the results, four subjects showed an effect on the reduction of sleep latency. Two of those showed the effect to retraction phenomenon from the variation of HR and PNS.