A brake-aiding device applicable to a two-wheeled vehicle, the brake-aiding device comprising: a casing, being a hollow member; a drive mechanism, being installed in the casing and comprising a revolving axle (30, 40), and a first revolver (31, 41), a second revolver (32, 42) and a driven revolver (33, 43) that all three are configured to rotate against the revolving axle (30, 40), wherein the driven revolver (33, 43) has at least one propping portion (335, 435) for providing forward or backward stop to the first revolver (31, 41) and the second revolver (32, 42), so that when any of the first revolver (31, 41) and the second revolver (32, 42) rotates forward or backward, the driven revolver (33, 43) is driven to rotate, wherein the first revolver (31, 41), the second revolver (32, 42) and the driven revolver (33, 43) each have a rear segment mounted around the revolving axle (30, 40), so that front segments of the first revolver (31, 41), the second revolver (32, 42) and the driven revolver (33, 43) are allowed to move up and down inside the casing within a predetermined range, wherein the front segments of the first revolver (31, 41) and the second revolver (32, 42) are for cables (L, R) of two brake levers of the two-wheeled vehicle to connect, and the front segment of the driven revolver (33, 43) is for cables (FW, RW) of front- and rear-wheel brakes of the two-wheeled vehicle to connect, characterised in that the revolving axle (30, 40) is transversely provided near a rear end of the casing, and a distance (d) between where the driven revolver (33, 43) connects the front-wheel brake cable and the axle (30, 40) is smaller than a distance between where the driven revolver (33, 43) connects the rear-wheel brake cable and the axle (30, 40), wherein the casing has a top and a bottom each provided with two through holes (111, 112), and the cables (L, R) of the two brake levers and the cables (FW, RW) to the two brakes are connected to the drive mechanism from the top and bottom of the casing through the through holes (111, 112), and wherein the revolving axle (30, 40) is formed by two shafts (301, 401) that are coaxial and pass through two lateral sides of the casing. a casing, being a hollow member; a drive mechanism, being installed in the casing and comprising a revolving axle (30, 40), and a first revolver (31, 41), a second revolver (32, 42) and a driven revolver (33, 43) that all three are configured to rotate against the revolving axle (30, 40), wherein the driven revolver (33, 43) has at least one propping portion (335, 435) for providing forward or backward stop to the first revolver (31, 41) and the second revolver (32, 42), so that when any of the first revolver (31, 41) and the second revolver (32, 42) rotates forward or backward, the driven revolver (33, 43) is driven to rotate, wherein the first revolver (31, 41), the second revolver (32, 42) and the driven revolver (33, 43) each have a rear segment mounted around the revolving axle (30, 40), so that front segments of the first revolver (31, 41), the second revolver (32, 42) and the driven revolver (33, 43) are allowed to move up and down inside the casing within a predetermined range, wherein the front segments of the first revolver (31, 41) and the second revolver (32, 42) are for cables (L, R) of two brake levers of the two-wheeled vehicle to connect, and the front segment of the driven revolver (33, 43) is for cables (FW, RW) of front- and rear-wheel brakes of the two-wheeled vehicle to connect, characterised in that the revolving axle (30, 40) is transversely provided near a rear end of the casing, and a distance (d) between where the driven revolver (33, 43) connects the front-wheel brake cable and the axle (30, 40) is smaller than a distance between where the driven revolver (33, 43) connects the rear-wheel brake cable and the axle (30, 40), wherein the casing has a top and a bottom each provided with two through holes (111, 112), and the cables (L, R) of the two brake levers and the cables (FW, RW) to the two brakes are connected to the drive mechanism from the top and bottom of the casing through the through holes (111, 112), and wherein the revolving axle (30, 40) is formed by two shafts (301, 401) that are coaxial and pass through two lateral sides of the casing.