A physical activity reference value for health promotion, 23 METs-h/week was established by the Ministry of Health, Welfare, and Labour in Japan in 2006. The purpose of this study was to determine the daily step counts (steps/day) that classify adults as meeting the 23 METs-h/week reference value by using objective measurements. Objectively measured physical activity levels of 1837 Japanese adults aged from 23 - 69 yrs from both urban and rural Japanese cohorts were provided. Amount of physical activity and daily step counts were assessed using a triaxial accelerometer (Actimarker EW4800; Panasonic Electric Works). Receiver operating characteristics (ROC) curve analysis determined the optimal daily step counts (steps/day) that discriminated adults who met the reference value from those who did not. Approximately 48 % of Japanese adults met the 23 METs-h/week of physical activity reference value. ROC curve analysis found that 9341 steps/day produced 77.1 % of sensitivity and 79.5 % of specificity in all subject. When the analysis was performed in each cohort, 9980 steps/day and 8640 steps/day were indicated as the optimal daily step counts for them to meet 23 METs-h/week in urban and rural cohort, respectively. These data suggest that Japanese adults are likely to meet 23 METs-h/week of physical activity reference value if they accumulate between 8500 and 10,000 steps/day of daily step counts.