The International Physical Activity Questionnaire (IPAQ) is a self-reported questionnaire for assessment of physical activity and has been validated in many countries among adults. However, there are few studies about the validity of IPAQ for children. The purpose of this study was to investigate the validity of moderate to vigorous physical activity according to the modified version the IPAQ for Japanese Early Adolescents (IPAQ-JEA). Ninety-two adolescents aged 10-13 years participated in this study. The validity of the IPAQ-JEA criteria was tested using an activity monitor (Active style Pro, HJA-350IT; ASP). Daily physical activity was continuously monitored for one week by ASP. The participants were asked to complete the IPAQ-JEA after wearing the ASP. The epoch length of ASP was set at 1-min in this study (ASP_1-min). According to the minute by minute METs values, time spent on moderate intensity physical activity (MPA, 3 to 6 METs), vigorous intensity PA (VPA, > 6 METs), and moderate to vigorous intensity PA (MVPA, > 3 METs) was calculated. In addition, we also calculated bout physical activity maintained for 10 minutes or longer (ASP_bout). Weekly time spent on MVPA assessed by IPAQ-JEA (MVPA_IPAQ-JEA) was significantly correlated with that assessed by ASP_bout (MVPA_ASP_bout) (ρ=0.359, p<0.01) and ASP_1-min (MVPA_ASP_1-min) (ρ=0.399, p<0.01). However, MVPA_IPAQ-JEA was significantly higher than that of MVPA_ASP_bout and MVPA_ASP_1-min (p<0.001). Although time spent on VPA assessed by IPAQ-JEA (VPA_IPAQ-JEA) was also significantly correlated with that assessed by ASP_bout (VPA_ASP_bout) (ρ=254, p<0.05) and ASP_1-min (VPA_ASP_1-min) (ρ=438, p<0.01), time spent on VPA_IPAQ-JEA was significantly higher than that for VPA_ASP_bout and VPA_ASP_1-min (p<0.001). These results support the use of the IPAQ-JEA as a relative measure of physical activity among 10-13-year-old children.