A changeover operation device, for changing over the positions of at least two components to establish three or more speed modes in a speed changer mechanism accommodated within a housing having an opening, includes operation handles arranged in a corresponding relationship with the components. Each of the operation handles is movable between two specified positions along a specified operation direction to change over the positions of the components. The operation handles are continuously arranged within the opening of the housing, one of the operation handles being partially overlapped with the other.