We proposed a new ankle-foot orthosis using elastomer-embedded flexible joints (EEFJ), composed of C-shaped springs and 3D-printed circular elastomer. This orthosis was designed to reduce burden on the tibialis anterior muscle (TA) and to achieve clearance between the tip of the toe and the ground. Strength testing, and gait analysis were conducted for the orthosis. According to the results of strength testing, the combination of the C-spring with 0.3 mm and 0.5 mm thickness and the elastomer with 30% and 60% filling density performs a supporting torque of 0.7-2.3 Nm to plantarflexion. In contrast, torques in the other directions were relatively small. According to the results of gait experiments in seven healthy young subjects, the proposed orthosis successfully reduced the TA activation on initial contact and in the swing phase, and range of motion on initial contact.