To provide a device and a method for forming a bent hole in a concrete foundation for forming a bent hole bent at a predetermined angle to allow various pipes such as drain pipes to be inserted therein between the outer vertical surfaces of the concrete foundations (outer surfaces of rise parts) and the inner horizontal surfaces thereof (surface of inner mat foundation or surface of floor concrete part) of various buildings constructed by using molds.

This device comprises a pair of sleeves 2, 3 formed by so winding base sheets 9a, 9b in a hollow cylindrical shape as to be expanded and contracted and having elliptic opening parts 3a, 3a formed at one end and sleeve opening retaining devices 4, 5 fitted to opening parts 2b, 3b at the other ends of the sleeves 2, 3. In this method, the elliptic opening parts 2a, 3a of the sleeves 2, 3 are fitted and fixed to each other to continuously connect the pair of sleeves 2, 3 to each other at a predetermined angle.