a key factor in the relationship between OJ and insomnia. These findings might provide useful information for preventing the adverse effects of insomnia. (J Occup Health 2015; 57: 142-150) Key words: Insomnia, Organizational justice, Psychosocial factorOrganizational Justice (OJ) has been a notable psychosocial factor in the workplace for the past 10 years. Low perceived OJ is reported to be associated with a variety of health problems, such as selfrated poor health 1) , psychological distress 1−5) , depression 6) and coronary heart disease 7) . The concept of OJ consists of four components 8) , the most acknowledged of which is distributive justice, an assessment of the fairness of outcome allocation 9) . The second component is procedural justice, which is fairness derived in the process of decision evaluation 10,11) . It has been reported that perceptions of procedural justice are often influenced by interactional elements, which can be seen as the other two dimensions of justice: interpersonal justice and informational justice. Interpersonal justice refers to respect and sensitivity aspects of interactional elements, which assesses the dignity and respect received from managerial authority. Informational justice, however, is an explanatory aspect of interactional elements, which assesses the degree of explanations from managerial authority 12,13) . Until recently, research on OJ has examined the unique effects of each justice perception separately on various outcomes. However, lately, research considering all justice components simultaneously has increased, as it might provide a more comprehensive understanding of justice 14) . At this time, there are very few studies that have investigated the relationships among all four justice components and health problems.Insomnia is one of the most common health problems worldwide 15) . It can be related to a variety of Cross-sectional self-reported questionnaire data from 1,893 employees (92.2% of subjects) were collected. OJ was measured using the Japanese version of the OJ questionnaire, which has four components (distributive, procedural, interpersonal and informational). Insomnia was assessed with the Athens Insomnia Scale. Logistic regression analysis, with insomnia as a dependent variable and OJ as an independent variable, was conducted. Results: Subjects with low overall OJ had a higher risk of insomnia (adjusted odds ratio (AOR), 2.37; 95% confidence interval (CI), 1.59 to 3.53) and two insomnia symptoms (AOR of 2.47 and 95% CI of 1.68 to 3.65 for sleep induction problem; AOR of 1.73 and 95% CI of 1.21 to 2.48 for sleep maintenance problem). The four justice components were all associated with insomnia and sleep induction problems. Sleep maintenance problems were associated with only the distributive justice component. Conclusions: All four justice components were associated with both insomnia and sleep induction problems. Sleep maintenance problems, however, showed different features. Specifically, the distributive justice component seemed to be