The purpose of this study was to examine vocational identity formation of young adult workers from the standpoint of workplace relatedness. “Workplace relatedness” was defined as the perception of relationships between oneself and the others, focusing on relatedness in the workplace interpersonal context. Seven young adult workers were interviewed to explore the structure of workplace relatedness, from the individual’s point of view. Based on these results, a questionnaire was given to men and women in their 20’s working at a various organizations in Japan (N = 208), in order to determine the influence of workplace relatedness on vocational identity through formation factors (internalization, self-awareness, openness to learning). The major findings were as follows: (1) workplace relatedness were constructed by six factors (leadership, partnership, self-control, recreation, similarity, affinity); (2) leadership directly influenced vocational identity; and (3) leadership, self-control, and similarity affected vocational identity through self-awareness (reflection) and openness to learning (pursuing opportunity).