PURPOSE:To provide a shield advancing excavator for excavating a rectangular cross-section which has a simple mechanical structure, high earth removal efficiency, and superior adaptability to pressure holding type and open type shields. CONSTITUTION:A partition wall 2 partitioning a lateral rectangular cross-sectional cylindrical skin plate 1 into a front chamber F and a rear chamber B is installed. A plurality of swing arms 4 penetrating the partition wall 2 are oscillationally pivoted around the same shaft center to provide a first cutter drum 6a between the front ends of the swing arms 4. Second cutter drums 6B in which shaft centers decline forward when compared with the first cutter drum 6A are rotatably provided at the opposite sides to excavate the fronts of the front ends of the swing arms 4 by the inside outer peripheral edge front sections of the second cutter drums 6B. The swing arms 4 are oscillated by oscillation driving cylinders 7 in the rear chamber B to excavate a rectangular cross-sectional tunnel corresponding to the cross section of the skin plate 1 by the first and the second cutter drums 6A, 6B.
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