Enhancing the physical activity level has become a significant issue for the Japanese to prevent lifestyle-related diseases. For developing a simple and valid method to assess daily energy expenditure, we measured the energy expended by several physical activities in 13 young Japanese adults using the portable expiration gas metabolic monitor. Each subject wore a heart rate monitor on the chest and three-dimensional accelerometers on the wrist, waist and ankle. The energy expenditure was correlated with the heart rate and with the acceleration at the wrist, waist and ankle. Energy expenditure showed higher correlation coefficients with the acceleration at the waist and ankle than at the wrist. A multiple regression analysis showed that the energy expenditure could be estimated from the accelerations at the wrist and waist, the heart rate, gender, height and weight. The results indicate that measuring both the body acceleration and heart rate was important for developing a simple and valid method to assess daily energy expenditure.