To fix two half cylinders without looseness in a short time, in an excavation casing of a division opening and closing type in which a cylindrical body is two-divided in the axial direction, the divided half cylinders are connected with each other by a hinge such that the cylindrical body can be opened and closed, free ends (not on the hinge side) of the half cylinders are detachably connected with each other by connection metal fittings.

A casing has pins 13 protruded from the outer surface of the free end side of each of half cylinders 11, each of the pins 13 having a flange 14 on its head. Each of connection metal fittings 2 has a first pin hole 21 and a second pin hole 24 through which the pins can pass respectively and which are opened at the same interval as that between the pins 13, and a notch is downward opened from the second pin hole 24 to form an opening part 25. The first pin hole 21 of the connection metal fitting 2 is hung on the right side pin 13 and the connection metal fitting 2 is turned with the right side pin 13 as an axis to pass the left side pin 13 through the opening part 25 to hang the second pin hole 24 on the left side pin 13 from above, thus connecting the half cylinders 11 with each other.