To predict the collapse of a bedrock accurately and positively by listening to the small collapse sound of a rock due to the warning phenomenon of a bedrock collapse accurately and positively.

A device has high-sensitivity acceleration sensors 1a-1d buried into a bedrock, an AE measuring instrument 3, a speaker 4, a communication line 5, a personal computer 6, and a digital tape recorder 7. Then, by listening to a detection signal sound from the speaker 4, it is predicted to be an initial stage where the bedrock is slightly cracked when the frequency of the collapse sound of the bedrock is high and the sound level is small, it is predicted that the crack of the bedrock progresses when a large sound as in the case when a crack surface is rubbed, and it is predicted that the collapse of the bedrock approaches when the interval of the collapse sound heard due to the progress of the above crack is small and can be frequently detected. Also, the number of occurrence of the collapse sound by an AE measuring device 3 and the operation result of an amplitude distribution are displayed on a CRT, thus graphically displaying the aging of the bedrock collapse.