SHIELD MACHINE

PURPOSE:To smoothly drill the periphery of an existing tunnel for the expansion or the like of the cross section thereof, using a rotary mechanical cutter and according to a sealed shield driving method. CONSTITUTION:This shield machine has a rotary cutter 10 laid so as to surround an existing tunnel 90 having circular cross section for drilling the periphery thereof including the wall of a segment 91, a drive source 20 for the cutter 10, a jack 25 for obtaining a thrust force under a pushing force applied to the rear section thereof and others. The innermost cutter bit 12 of the cutter 10 is laid so as to cut an area several ten millimeters outside the external surface of the segment 91 of the tunnel 90 for forming cylindrical surface 94 directed outward. Also, a seal member 30 along the surface 94 is fitted to the inner surface of a division 3 separating the cutter 10 from the drive source 20 thereof or the jack 25 at a position behind the cutter 10.