To provide a hard-rock layer excavator capable of excavating a hard rock layer by a simple facility.

The hard-rock layer excavator has a roll-drive mechanism having a kelly-bar 10 inserted into a pit hole excavated up to a hard rock layer while rotating and driving the kelly-bar 10. An excavating tool 20, in which cutters 30 are mounted on the outer circumference of a shaft 26 turned around a shaft crossed at right angles with the kelly-bar 10, is set up at the front end of the kelly-bar 10. In the excavating tool 20, a plurality of the cutters 30 are fitted on the outer circumference at regular intervals while scrapers 32 scooping up excavated chips are attached among the cutters 30, and a bucket, into which excavated chips in the scrapers 32 are charged with the rotation of the excavating tool 20, is installed at that time.