To provide an excavator capable of dispensing with large-scaled equipment and reducing a work rate to solve a conventional excavator such that it needs the large-scaled equipment and it is difficult to be used in astronomical exploration.

This excavator 1 comprises an approximately cylindrical device body 4, a rotary cutter 2 mounted on one end of the device body 4, and an expandable body 5 mounted on an outer peripheral face of the device body 4. The expandable body 5 is expanded and closely pressed to an inner wall of a borehole, whereby the reaction force in pressing and rotating the rotary cutter 2 can be supported by a comparatively simple structure, and the excavator can be effectively used in astronomical exploration.