A gear-shift-operation transmission device for a saddle-ride type vehicle, comprising: an input-side member configured to be connected to a shift pedal; an output-side member configured to be connected to a gear-shift operation unit of a transmission body; reaction-force generating means for exerting a force between the input-side member and the output-side member; and a displacement detection sensor (39A, 39B) configured to detect a relative displacement; wherein the reaction-force generating means comprises: a cam groove provided to at least one of the input-side member and the output-side member, and having a compression-side inclined surface and a tension-side inclined surface whose inclinations are different from each other with a neutral line interposed therebetween; a pressing member (34, 41) provided to the other of the input-side member and the output-side member, and configured to be elastically pressed against the cam groove; and characterized in that the reaction-force generating means is configured to exert a compressive reaction force and a tensile reaction force between the input-side member and the output-side member; that the displacement detection sensor (39A, 39B) is configured to detect a relative axial displacement between the input-side member and the output-side member against the reaction force from the reaction-force generating means; and that the compression-side inclined surface and the tension-side inclined surface are set to have different absolute values of inclination angles to a center axis of the input-side member. an input-side member configured to be connected to a shift pedal; an output-side member configured to be connected to a gear-shift operation unit of a transmission body; reaction-force generating means for exerting a force between the input-side member and the output-side member; and a displacement detection sensor (39A, 39B) configured to detect a relative displacement; wherein the reaction-force generating means comprises: a cam groove provided to at least one of the input-side member and the output-side member, and having a compression-side inclined surface and a tension-side inclined surface whose inclinations are different from each other with a neutral line interposed therebetween; a pressing member (34, 41) provided to the other of the input-side member and the output-side member, and configured to be elastically pressed against the cam groove; and a cam groove provided to at least one of the input-side member and the output-side member, and having a compression-side inclined surface and a tension-side inclined surface whose inclinations are different from each other with a neutral line interposed therebetween; a pressing member (34, 41) provided to the other of the input-side member and the output-side member, and configured to be elastically pressed against the cam groove; and that the reaction-force generating means is configured to exert a compressive reaction force and a tensile reaction force between the input-side member and the output-side member; that the displacement detection sensor (39A, 39B) is configured to detect a relative axial displacement between the input-side member and the output-side member against the reaction force from the reaction-force generating means; and that the compression-side inclined surface and the tension-side inclined surface are set to have different absolute values of inclination angles to a center axis of the input-side member.