PURPOSE: To avoid the occurrence of water leakage in a simple constitution by forming a bracing element provided on a bracing shield by plural pressure hoses, and continuously enlarging the circumference by expansion.

CONSTITUTION: A self-advancing shield tunneling machine includes one control shield 1 to which a cutter unit is journalled and at least two bracing shields 2, 3 connected to each other by feed cylinders 6, 9. Bracing elements 7, 11 provided on the first and second bracing shields 2, 3 are formed by plural elastic pressure hoses. The pressure hose is disposed round the outer periphery of a closed shield structure, and the circumference can be enlarged continuously by expansion. Thus, the generation of a gap when the bracing elements 7, 11 are moved outwardly in the radial direction is avoided to prevent water leakage.