When an object is touched, the properties like shape, temperature, rigidity, texture and weight should be perceived. As a basic research of human tactile, it is most important to know how humans could perceive the shape of the object by fingers. Thus length and contacting curvature of an object are thought to provide important perception information. But there are scarce perception studies using changed delay time on length discriminative experiment. In present study, to investigate the changed delay time during length discrimination experiment with thumb and forefinger for working memory, we develop a tactile length interface device for the experiment. We also divide the experimenters into two groups, the young people and old people to discuss that when we become older whether our performance on length discrimination drop down or constant.