A shield type hydraulic tunnel boring machine having means for detecting an occurrence of excess excavation due to accidental collapse in tunnel face ground apt to occur during tunnel boring through soft and unstable ground and for further determining the location, shape, scale and the like of such excess excavation occurred is provided. The means comprises optimumly a plurality of rod-shaped members capable of being extended out of and retracted into the machine. Amounts by which these members are paid out until they reach ground wall of any cavity due to the occurred excess excavation are measured to determine the actual state of such cavity. The means is provided preferably at a plurality of proper positions on a shield body of the machine and respective values of the measured amounts at these positions are recorded and displayed, whereby the location, shape, scale and the like of the occurred excess excavation can be confirmed.