To secure the quality of a cast-in-place pile by decreasing a change in the water level of hole wall slurry, when the cast-in-place pile is constructed by an earth drill method.

This casing tube A for the earth drill method is constituted by forming a bypass path B through which the hole wall slurry 4 lifted to the outside of a steel pipe 1 for a casing by a drilling bucket 3 flows back into a drilled hole below the drilling bucket 3. The bypass path B is formed of a plurality of pipes 2 which are fixed to the outer periphery of the steel pipe 1 for the casing and both the upper and lower ends of which are communication-connected to an internal space of the steel pipe 1 for the casing, or formed by making the steel pipe 1 for the casing employ a double pipe structure and communicating both upper and lower ends of a gap, formed between the inside and outside steel pipes 1a and 1b, with the internal space of the inside steel pipe 1a.