To provide an overloading prevent device with which transmission of torque is surely interrupted when overload is generated and the interrupted state is maintained without slip or the and which is executed by a simple structure and at a low cost.

On one side of a drive shaft 1 and a driven shaft 2 which are arranged facing to each other on the same shaft center, a supporting part 10 where is projected to the other side is provided, and an outer sleeve 5 is fitted approximately concentrically on the outer peripheral side of the supporting part 10 between the drive shaft 1 and the driven shaft 2. An engaging part 8 and a part 17 to be engaged which is engaged so as to be freely engaged and disengaged to the engaging part 8 in the axial direction are respectively provided on the end-part side of the one side of the drive shaft 1 and driven shaft 2 and on the one end side of the outer sleeve 5 and an inclined surface which is inclined in the peripheral direction on at least one side of the engaging part 8 and the part 17 to be engaged is provided so that a component force in the detaching direction is generated on the outer sleeve 5 when transmitting the power. The other end part of the outer sleeve 5 is connected to the other side of the drive shaft 1 and the driven shaft 2 freely movably, and the outer sleeve 5 is held between the supporting part 10 and the outer sleeve 5 so that the engaging part 8 is engaged with the part 17 to be engaged, and holding means 18 for releasing holding of the outer sleeve 5 is provided so that the engaging part 8 and the part 17 to be engaged are disengaged at the time of overloading.