The experiment was conducted to test the effectiveness of majority opinion's reality on conformity in following three changing situations: (1) majority opinion formation period (2) unanimity period (3) breakdown period. Twenty female college students responded on a time perceptual task through 30 trials in one of the following two conditions: (1) high reality: Majority's opinion was less erroneous; (2) low reality: Majority's opinion was obviously erroneous. Major results were as follows. 1. In the early opinion formation periods, the conformity rates were equal in both reality conditions. But in the late opinion formation period when for the first time more than half of the group members agreed to the opinion, the conformity rates of only high reality condition increased radically. 2. In the opinion unaimity periods, the conformity rates of both conditions were not different. 3. In the opinion breakdown periods, under high reality condition the conformity behaviors tended to continue, whereas under low reality condition that tendency was not observed, suggesting that under high reality condition majority opinion will give the individuals more internal effects.