In adults’ behavior system, attachment behavior and reproduction behavior (sexual behavior) are correlated with each other. Thus, this study purposed to review previous studies on the relation between attachment and sexual behavior, specifically, sex crimes. In particular, this study was focused on child sexual abuse and rape among sex crimes. Sex offenders showed markedly stronger unstable attachment than ordinary people, and they showed stronger unstable attachment to their mother than other types of criminals. In stressful situations, they operated their reproduction behavior (sexual behavior) inappropriately rather than their attachment behavior. Sex offenders appeared to distrust themselves and others and to have difficulty in establishing intimacy. Furthermore, they were found to be deficient in sympathy for understanding others and to have distorted perception of themselves and others.