A rotary face plate is simply configured by including only a machine mechanism for rotating it on its axis. In order to achieve the configuration, a swing arm for a rotary blade is mounted on one side of the rotary face plate whereas a driving motor and a swing motor for the rotary blade in each of the swing arms are independently mounted on each of the swing arms on the other side. One side has only a function of rotating and cutting on the boundary of the face plate, and therefore, cutting chips can be remarkably readily removed. Only a rotating motor for a drive source is mounted on the other side. As a consequence, a round tube or a square tube having a square cross section can be cut only by controlling the motor for rotating the rotary face plate at a required angle.