The purpose of this study was to investigate the age difference of children's evaluation of problem solving process. Ss were twenty-one second graders, nineteen third graders and twenty-four fifth graders. The task consisted of five pictures depicting five steps in which a model student solved a mathematics word problem. Four sets of tasks were designed so that each task included an error at four different steps. Subjects were presented with covered material pictures and were asked to uncover the pictures they want to look, and to evaluate whether the given problem solving process was correct. The Main results were as follows : 1) Second and third graders looked less at the step which presented a result than at other steps.No such difference was found in the fifth graders.2) Second and third graders detected less errors when the error was in the step which presented a result, than when the error was in the other steps; no such difference was found in the fifth graders.