Abstract: 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 works 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 ultrasonic wave transmitting and receiving devices disposed as spaced at least along a radial line on the front surface of a substantially disk shaped rotary cutter head of the machine for transmitting ultrasonic waves in forward and upward directions and receiving reflected waves from tunnel face ground wall, a wave transmission and reception controlling means, and a transmission-to-reception time interval detecting means for determining distances from the respective wave transmitting and receiving devices to the ground wall.