To prevent interruption between a work machine and a machine main body with a simple mechanism.

There are provided an alarming means and/or an actuator operation stop means. A first limit switch 13 which is switched on and off by a vertical motion of a first boom 1 and a second limit switch which is switched on and off by right and left motion of a second boom 2, a third limit switch 33, which is switched on and off by the vertical motion of an arm 3 and a fourth limit switch 43 which is switched on and off by a rocking motion of a work machine (bucket 4) are connected to an alarm generation means and or an actuator operation stop means. With all the limit switches 13 to 43 arranged to be in a closed state, the alarm generation means and or the actuator operation stop means are operated.