Abstract: A transmission device adopted for a working tool such as a weed cutter having an engine, a rotary blade, and a gear case for supporting the rotary blade. The transmission device comprises an operation pipe for connecting the engine with the gear case, a transmission shaft disposed inside the operation pipe to transmit the torque of the engine to the rotary blade, and a bearing pipe interposed between the operation pipe and the transmission shaft. The inner surface of the bearing pipe contacts with the outer surface of the transmission shaft to support the transmission shaft rotatably. A plurality of grooves are formed circumferentially on the inner surface of the bearing pipe with predetermined intervals to reduce the contacting area thereof with respect to the transmission shaft. The transmission device further comprises a vibration isolator which is fixed to an end of the operation pipe and removably engaged with a clutch housing of the engine.