A multistage transmission is provided to vary the torque of the input gear assembly by selectively changing the bevel gear of the output transmission assembly combined with the bevel gear of the input transmission assembly. An input gear assembly(1) comprises a plurality of input gears(12-15) arranged to the axial direction. An output gear assembly(2) comprises a plurality of output gears arranged to the axial direction. An input transmission assembly(3) is engaged with the input gear of the input gear assembly. The input transmission assembly is pivotally installed at a supporting shaft(30). An output transmission assembly(4) is engaged with the output gear of the output gear assembly. An input synchro(5) is comprised of a plurality of synchro rings. Each synchro ring comprises the key protrusion inserted into the key groove of the input gear. An output synchro(6) is comprised of a plurality of synchro rings.
