PURPOSE: To simply and certainly prevent flooding in an excavating machine in the case when the open shield excavating machine is divided into a front excavating machine in to he front and a tail excavating machine in the rear and they are freely engaged with each other free to slide.

CONSTITUTION: The inside of a front excavating machine 2 is partitioned into the front and the rear with a partition wall 11, and a first press angle 6 arranged between a propulsive jack 3 of a front excavating machine and the front edge of a tail excavating machine 3 and a second press angle 7 arranged between a propulsive jack 5 of the tail excavating machine 3 and an underground structure 8 to hang down in this tail excavating machine 3 are to be expandable in diameter with a giraffe jack 12 interposed in the middle of upper and lower crosspieces constituting a rectangle frame body. Then, a plate type seal material 13 is attached on the outside faces of right and left vertical members and the crosspieces below, and additionally, an elastic water stop plate 15 is interposed between the rear face of the first press angle 6 and the front edge of the tail excavating machine 3.