The invention relates to a seeder, which comprises a variable transmission mechanism, wherein a tensioning device is arranged in the variable transmission mechanism and is used for pushing and pressing a transmission belt; the transmission belt is sleeved on a change wheel A and a change wheel B; the change wheel A and the change wheel B are belt pulleys with combined tapered structures and are arranged in opposite directions; and the tensioning device has a roller type structure. Because of the seeder, the phenomenon of looseness and sliding between the transmission belt and the belt pulleys during movement can be prevented, and the service life of the transmission belt is prolonged. The seeder has the characteristics of simple structure and good using effect.