Entrainment of circadian behavior rhythms by daily exposure to running-wheel was examined in mice under constant darkness. Spontaneous movement was individually monitored for more than 6 months by thermal sensor. After establishment of steady state free-running, mice were placed in a different cage equipped with a running-wheel for 3 h once per day at 6:00 am. The daily exchange was continued for 80 days. The number of wheel revolutions during exposure to running-wheel was also measured simultaneously with spontaneous movement. In 13 out of 17 mice, circadian behavior rhythm was entrained by daily wheel exposure, showing a period indistinguishable from 24 h. The entrainment occurred in parallel with an increase in spontaneous movement immediately prior to the daily wheel exposure. A similar pre-exposure increase was observed in only one out of 4 un-entrained mice. The pre-exposure increase appeared in 19.5 days on average after the start of daily wheel exposure and persisted for 36 days on average after the termination of the exposure schedule. The pre-exposure increase was detected only when daily wheel exposure came into the activity phase of the circadian behavior rhythm, which was accompanied by an increase in the number of wheel-revolutions. These findings indicate that a novel oscillation with a circadian period is induced in mice by daily exposure to running-wheel at a fixed time of day and suggest that the oscillation is involved in the non-photic entrainment of circadian rhythms in spontaneous movement.