Collective Efficacy (CE), which was proposed by Bandura (1997), is one of the most important factors for understanding the function of a group or organization. Moreover, CE is an important factor to consider when evaluating “team performance” (Uchiyama, 2001). However, in the field of coaching, no practical study using a measure of CE has yet been conducted. Therefore, the present study was performed to verify the effectiveness of coaching using CE theory to evaluate and confirm agreed-upon items that reflect team performance. In the present study, the CE of a basketball team was evaluated using the Collective Efficacy Scale for Half-Court Offense (CES-HCO). In order to examine the effectiveness of coaching, improvement of team performance was measured using the number of turnovers for each possession. The key findings of this study were as follows. 1)  Factor analysis revealed that the CES-HCO comprised 20 items within the following frameworks of adjustments and characteristics. Moreover, with a Cronbach's α and a test-retest correlation coefficient, r, of .71 ( p <.001), the CES-HCO was confirmed to have high reliability. 2)  Using the “theme-do-reflection cycle” (Uchiyama, 2001), a coaching program that incorporated the use of the CES-HCO was developed. During the intervention period, the coaching program significantly increased the CES-HCO score ( p <.05). 3)  Using this coaching program that incorporated the CES-HCO, team performance improved significantly during the intervention period ( p <.05). The results of this study indicate that the practical application of CE is useful for reinforcing improvement of team performance in basketball through coaching.