A processing machine includes a machine bed, a spindle seat, a sliding rail unit, and a driving unit. The sliding rail unit is disposed between the machine bed and the spindle seat. The driving unit is used for driving the spindle seat to move within a slot in the machine bed, and includes a threaded rod journalled on a junction between a bottom wall surface and a lateral wall surface of the machine bed, and a nut member disposed fixedly on a junction between a bottom surface and a lateral side surface of the spindle seat and engaging the threaded rod.