Typical human-based biped robot has 12-DOF for its legs, but there may be another approach not to take a model on human, but to design function oriented. To design a practical light-weight biped, reducing a number of DOF is one of the most efficient method. This paper discusses minimum number of DOF for various cases, where 4, 7, 5 is the resultant minimum number of DOF for horizontally composed terrain, uneven terrain with normal leg exchange sequence, uneven terrain with partial leg exchange sequence, respectively. This paper also shows practical designs of bipeds with 5, 8, and 6-DOF. Trial manufactured machines based on these discussions could show good performances on stairs and uneven terrain.