PURPOSE: To make compatible the improvement in the excavation efficiency of soil and safety by simple facilities by spraying compressed air against the surface of the soil of the peripheral section of an excavated pit while pushing and demolishing soil at a central section by mechanical power and sucking and discharging soil and sand generated.

CONSTITUTION: A compressed-air supply duct 20 having a nozzle 21 on the inside of the sidewall 11 of a cylindrical body 10 is installed as an excavator, the driving shaft 31 of an auger 30 with a cutting blade 33 is pivotally supported rotatably to the central opening section of an upper plate through a bearing 14, and a duct mounting port 15 connected to an evacuation-device connecting duct 17 is mounted to another opening section. The lower end of the sidewall 11 is pushed against so as to be slightly inserted into soil, and compressed air is sprayed against soil and soil is pushed and demolished. The cutting blade 33 is turned in conformity with the settling of the cylindrical body 10, and soil at a central section is pushed and destroyed while soil and sand generated by the pushing and destroying is lifted and forwarded to an upper section. Soil and sand are carried away to the outside of a system through the duct mounting port 15 and the duct 17 together with compressed air, and the formation of an excavated pit is promoted.