PURPOSE: To make it possible to excavate a tunnel having a rectangular section by driving cutters arranged in a forward direction at specific intervals to reciprocate in the direction of the cutter arrangement, and introducing excavate earth from spaces between the cutters.

CONSTITUTION: A shield device M is placed in the ground to arrange longer cutters in a forward direction at specific intervals in a state to press the cutters 1 against a facing, and they are operated in driving section. Face boards 10 are reciprocated up and down in the direction of the cutter arrangement, and a facing bedrock is excavated with the cutters 1. After that, excavated earth is moved backward of a taking-in device M in a chamber C from slits 11. According to the constitution, uniform excavation can be carried out.