To automatically and safely enable the effective stop of a rotary working machine by lifting a handle when turning an administration machine during the practice of tillage operations in a field.

This device for automatically stopping a rotary working machine of an administration machine comprises a handle arranged extendedly from an upper part of a transmission case 2 axially installing both wheels to the rear of a machine body and the rotary working machine connected to the rear of the machine body. In this case, a clutch unit 6 capable of connecting and disconnecting the power transmission to a transmission shaft 4 and performing changeover operations with a fork 5 is transmitted and connected to the transmission shaft 4 of the rotary working machine and a weight 8 rotatable in the front and rear directions of the machine body with a fulcral shaft 7 as the center is arranged in the upper part of the machine body. Furthermore, the side of the weight 8 is interlocked and coupled to the side of the fork 5 so as to enable the movement of the clutch unit 6 to the neutral position of the disconnected transmission by rotating the weight 8 to the front side of the machine body when the handle is lifted.