Daily walking keeps our body healthy. However, it is difficult to continue walking as a daily habit. To promote the habit of daily walking, we focus on the effect of team work. We often achieve big goals with others by working as a team and assisting each other. In this paper, we propose a system that helps users work as a team in daily walking. Our system uses a smartphone and a web application to allow users to see not only his/her own activity but also his/her team members' activities. We expected that seeing the exercise data of team members would encourage an individual to exercise. We held a one-month field trial in Nagahama City as a walking event. A total of 457 participants (96 teams and 85 individuals) were enrolled in the trial. Each participant was asked to walk 40km within 10 days, which is equivalent to 10,000 steps a day. At the end of the trial, 87 out of 96 teams achieved this goal. Analysis of participants' records for teams consisting of 5 members showed a difference in walking distance of over 20km among team members in 80% of the teams. This finding indicates that even though not all members of a team walked the same distance, they achieved the team's goal by sharing target distances according to their capability. Web access records show that 85% of the team participants watched his/her team members' activity more than once every 2 days. Participants' responses to questionnaires showed that 73% of team participants used communication within team members to motivate themselves. Additionally, the number of people who walk everyday increased even three months after the trial. These results suggest that the team effect has the potential to motivate members to continue their exercising activities.