An interlock mechanism includes a shift-and-select shaft a first fork, a second fork, a first inner lever, a second inner lever, an interlock member coaxially arranged around an outer circumference of the shift-and-select shaft while being allowed to rotate together with the shift-and-select shaft in the rotation direction as a unit and not allowed to be displaced in the axial direction, a first engagement portion formed on the first fork, a second engagement portion formed to project from the second fork, a first engaged portion formed to project from the inter lock member and engaged with the first engagement portion while the interlock member is positioned at a second rotation position and a second engaged portion formed on the interlock member and engaged with the second engagement portion while the interlock member is positioned at a first rotation position.