When do we begin to feel unpleasantness about being unable to reciprocate for help received? Do the reasons for unpleasant feelings when unable to reciprocate differ according to one's age and who provided the help? This study asked 2nd grade (n=121) and 4th grade (n=130) elementary school children on a questionnaire to estimate the importance of the reciprocity, the recognition of probability of reciprocity, unpleasant feelings when reciprocity is not accomplished, and the anger of the person whose help was not reciprocated. In this experiment, there were two conditions of help: from friends and from parents. When a parent had helped, the 2nd graders' unpleasant feelings was less than it was for 4th graders. When the helper was a friend, there were no differences in unpleasant feelings between 2nd and 4th graders. In addition, unpleasant feelings among 2nd graders was related to the possibility of helper's anger when reciprocity was not unaccomplished. Among 4th graders, however, the unpleasant feelings in the context of unaccomplished reciprocity were related to the importance of reciprocity and the recognition of probability of reciprocity. The study suggests that children come from the 4th grade to feel unpleasantly when reciprocity is not fulfilled, based on the norm of reciprocity.