PURPOSE: To improve accuracy in excavation with an excavator suspended from a crane by detecting the depth, twist and inclination of the excavation to indicate them in real time to an operator's cab.

CONSTITUTION: An excavator 1 having a bucket 2 is suspended from a crane 3 through a guide sheave 4. Next, the sheave 4 is provided with a rotary encoder 5 for detecting the depth of excavation. Then, the excavator 1 is provided with a mechanism 6 like an optical gyroscope for detecting the twist of the excavator itself and a mechanism 7 for detecting the inclination of the same. Further, an operator's cab 8 is provided with a processing section 9 for processing respective detecting signals in real time and a visual display section like a CRT display for indicating the process result. In excavating a channel for constructing an underground wall, an operator controls the operation of the excavator 1 with reference to the display on the display section in real time, so that the excavating condition can be grasped in real time to control accuracy in the excavation with the high precision while the number of times of measuring the channel wall can be reduced to save labor.