In this study, the nature of safety climates at construction work sites and workers' safety attitudes was ascertained, and the effect of safety climates on workers' safety attitudes and work site safety was examined. A self-rating questionnaire prepared for this study was delivered to 300 employees who were working at construction sites and 300 foremen of affiliated companies. Eight factors were extracted for the safety climate of work sites. Similarly, by factor analysis, eight factors were obtained from workers' safety attitudes, including four factors representing positive aspects of safety attitudes and four negative safety attitudes. The scores of negative safety attitudes in companies with fewer labor accidents were smaller than those in companies with more accidents. Negative safety attitudes were affected by safety climate more than positive ones, and this tendency was more remarkable for foremen than employees. These results suggest the importance of promoting safety climates for raising workers' safety attitudes and work site safety by diminishing negative safety attitudes.