Abstract: In a tunnel excavator for tunneling by rotating a cutter head provided in front of a shield body to thereby excavate the working face of a tunnel using disk cutters attached to the front surface of the cutter head, the cutter head is composed of an annular beam, an arched main spoke provided across the annular beam and a plurality of arched sub-spokes radially provided thereon and disk cutter assemblies are detachably attached to the main spoke and sub-spokes, so that the disk cutter has a simple structure and the reaction force of excavation is broken up by the main spoke and sub-spokes to be transmitted to the annular beam. As a result, it is possible to provide a strong and durable cutter head which can be easily manufactured.