To provide a gear shift operation mechanism with excellent assemblage capable of reducing a production cost and the weight by reducing the number of part items.

A cutout groove 5 along the direction orthogonal to the axial direction of a shifter rod 2 is provided in the peripheral surface of the shift rod 2 movably operated in the axial direction. A stopper plate 7 installed on a transmission case 1 is engaged with the cutout groove 5 through play with a dimension equal to the length of the stroke of the shifter rod 2 to allow the shifter rod 2 to be slid by the amount of the play for preventing an overstroke.