To excellently prevent the inertial rotation of a PTO shaft generated when uncoupling a clutch to shut off the power transmission to the PTO shaft by a simple means.

A PTO transmission device has a transmission body to transmit the engine output and a brake disk to prevent the co-rotation on a PTO shaft, and comprises a brake spring to be interposed between the transmission body and the brake disk, foldable front and rear links to connect the transmission body to the brake disk, and a weight interposed between the front and rear links. The brake disk is pressed against a friction body by the brake spring force when the PTO shaft is rotated at a low speed, and the brake disk is separated from the friction body by the centrifugal effect of the weight when the PTO shaft is rotated at a high speed.