The purpose of this study is to discuss the effects of the relationships with the significant others at an early life stage on the development at a later life stage, from the viewpoint of life-span development. Based on a review of the articles studying the relationships with significant others, two aspects have been clarified: 1. The notion of linking secure relationships with specific significant others at an early life stage with later psychological adjustments seems insufficient to explain all the cases studied so far. 2. The factors that cause the continuity/discontinuity of the relationships with significant others have not yet been studied. The new notion of relatedness concerning the relationships with significant others, which is based on the viewpoint of identity development, is proposed to explain the mechanism causing the continuity/discontinuity.