To provide a pile proof stress measuring device for crane type pile construction machine capable of measuring an accurate pile proof stress with a simple structure.

In this pile proof stress measuring device for crane type pile construction machine including a connecting device interposed between a mast tip part of a crane provided in a pile construction machine and a rotating device for pile construction, a load sensor is attached to a pin pivotally fixing the connecting device at the mast tip part. The connecting device is composed of a clevis attached to the pin-type load sensor and a swivel provided within the clevis. The rotating force of the rotating device is not transmitted to the load sensor, and only vertical force acts thereon. A pile proof stress is measured by the measuring device provided within the machine body of the pile construction machine.