Walking exercise in forests, referred to as “shinrin-yoku, forest-air bathing and walking, ” has been attracting attention as a method for promoting mental and physical health utilizing the environment and topography of forests in the recent time. Walking exercise in forests has characteristics arising from the natural environment and topography of forests with beautiful trees, twittering of birds, and favorable fragrances of woods, etc. However, scientific verification of such specific effects is necessary in order to make walking an authentic method to health promotion. This study intended to physiologically investigate it from physical and scientific point of view. For this purpose, we determined chronological changes in energy consumed in walking exercise in forests with a portable oxygen intake measuring device, on the basis of data on the respiratory and circulatory systems such as heart rate and the amounts of ventilation and oxygen intake. The results suggested that the changes in these parameters showed the movement correlated with the changes in topography of forests, including the inclination and demonstrated that selection on the resting locations was related to the comfortable rhythm of walking. Furthermore, it was indicated that exercise loading to living body tended to increase in association with increases in the upward inclination, resulting that the energy consumed in walking was less though the amounts of exercise loading to lower limbs tended to be very large at a download inclination of 36.0 degrees or larger. This demonstrative study suggested that to determine chronological changes in physiological loading conditions related to the walking route was effective to establish promenades in order to perform comfortable and effective forest bath.