Well drilling bit and well drilling method using the same

A well drilling bit for drilling bedrocks, the well drilling bit comprising:

• a columnar bit body;
• and
• a drilling fluid flow path formed in the bit body to wash away drilled cuttings from at least one of a bottomhole and a periphery of the bit body,
• wherein:
• the flow path is provided with a venturi mechanism including a venturi tube having a reduced-diameter portion where a cross sectional area is reduced and configured to generate a decompression region around a tip of the bit body, the decompression region being more decompressed than a surrounding region by the Venturi effect, so as to locally cause decompression boiling of the drilling fluid in a vicinity of the bottomhole,
• the flow path includes a first flow path communicating the venturi tube with an outer surface of the bit body near the tip thereof, a second flow path communicating the venturi tube with an outer surface of the bit body except for the tip thereof, and a third flow path communicating the outer surface of the bit body near the tip thereof with the second flow path,
• the first flow path and the second flow path are configured to be switchable so that the other is closed when one is opened, and
• the venturi mechanism generates a decompression flow area by sucking the drilling fluid into the third flow path at a flow speed of the drilling fluid flowing in the second flow path when the second flow path is opened.