A plunging assembly of a driveshaft comprising: an outer housing having a bore having a plurality of outer ball grooves extending in a longitudinal direction; an inner shaft being disposed to be able to undergo relative movement in the longitudinal direction in the bore of the outer housing and having a plurality of inner ball grooves that are paired respectively with the outer ball grooves to form a plurality of ball tracks ; a plunging unit connecting the outer housing and the inner shaft to allow a plunging motion and a rotational power transmission between the outer housing and the inner shaft ; and a stopper that is provided in the bore of the outer housing to limit relative movement of the inner housing and the inner shaft in a direction in which the inner shaft is inserted into the bore , characterized in that the outer housing has a mounting hole communicating with the bore , wherein the stopper is a plug member that is inserted into the mounting hole in a state that a frontal end portion thereof is exposed to the bore , wherein the outer housing has an inclined surface connecting the bore and the mounting hole , wherein the plug member comprises: a shock absorbing portion located in the bore , a fastening portion inserted into the mounting hole , and a connecting portion connecting the shock absorbing portion and the fixing portion , and wherein an outer peripheral surface of the connecting portion is formed to be inclined so as to be in close contact with the inclined surface . an outer housing having a bore having a plurality of outer ball grooves extending in a longitudinal direction; an inner shaft being disposed to be able to undergo relative movement in the longitudinal direction in the bore of the outer housing and having a plurality of inner ball grooves that are paired respectively with the outer ball grooves to form a plurality of ball tracks ; a plunging unit connecting the outer housing and the inner shaft to allow a plunging motion and a rotational power transmission between the outer housing and the inner shaft ; and a stopper that is provided in the bore of the outer housing to limit relative movement of the inner housing and the inner shaft in a direction in which the inner shaft is inserted into the bore , characterized in that the outer housing has a mounting hole communicating with the bore , wherein the stopper is a plug member that is inserted into the mounting hole in a state that a frontal end portion thereof is exposed to the bore , wherein the outer housing has an inclined surface connecting the bore and the mounting hole , wherein the plug member comprises: a shock absorbing portion located in the bore , a fastening portion inserted into the mounting hole , and a connecting portion connecting the shock absorbing portion and the fixing portion , and wherein an outer peripheral surface of the connecting portion is formed to be inclined so as to be in close contact with the inclined surface . a shock absorbing portion located in the bore , a fastening portion inserted into the mounting hole , and a connecting portion connecting the shock absorbing portion and the fixing portion , and wherein an outer peripheral surface of the connecting portion is formed to be inclined so as to be in close contact with the inclined surface . <EOS>