To accurately detect that a suspended excavator has reaches the bottom of an objective hole to be excavated for a hole excavator with the handing up and down of the excavator.

A moving sieve 11 is interlocked with a second excavator, and a fixed sieve 12 is interlocked with a fixed frame 62 forming the upper part of a tower device 6. A hanging rope 7 let out from a winch 8 is wound on the moving sieve 11 and fixed sieve 12, and the front end section 7a is interlocked with an interlocking frame 61 provided to the excavator. A load cell 13 as a detection device is provided to an interlocking part between the fixed sieve 12 and fixed frame 62 to constitute a joint device between both of them. When the hanging rope 7 is let out to suspend the excavator, tensile force applied to the hanging rope 7 is always detected by the load cell 13, and when this tensile force becomes lower than tensile force set in advance, a decision signal informed of the fact that the second excavator reaches the bottom of an objective hole to be excavated is outputted.