Abstract: A shield tunnel boring machine having at its boring head a pressure-resisting mud kneading chamber defined by a bulkhead, wherein the bulkhead is divided into outer peripheral and central bulkhead parts. The outer peripheral bulkhead part is fixed to the inner periphery of a cylindrical shield. The central bulkhead part is made rotatable in association with a head-positioned rotary cutter as driven by a main motor. The sealing means required for the bulkhead is limited to seal one for a gap between the fixed outer peripheral bulkhead part and the rotatable central bulkhead part and the number of necessary related parts can be remarkably reduced.