To rapidly and surely determine a spring water state in bedrock without necessitating a complicated system.

A bore hole 1 is drilled in bedrock R below ground water level, a drain pipe 3 having a valve 4 and packers 2 are inserted into the hole, spring water in the hole is blocked by the packers 2, and thereafter the valve 4 of the drain pipe is opened to release the spring water in the hole, the relationship between the amount of the spring water and time is measured, and the presence state of cracks C having high permeability is determined by classifying a spring water pattern on the basis of the quantitative relationship among the maximum and steady values of the measured amount of the spring water and their respective predetermined threshold values.