A positive effect of trust on the level of cooperation has been repeatedly demonstrated in social dilemma experiments. However, such an effect of trust is expected only when members behave strategically. Since strategic considerations are less relevant in a situation with lower visibility of individual action, the effect of trust is hypothesized to diminish as visibility decreases. The hypothesis was tested in a 3-person iterated social dilemma experiment with feedback manipulation. The results of this experiment clearly supported the hypothesis. That is, trust by feedback interaction was significant, and simple main effect of trust was significant only in feedback condition, not in no feedback condition.