PURPOSE: To exactly judge the occurrence and degree of the liquefying of the sandy ground by applying a vibration to an oscillating plate in a square ground formed by two mutually facing side plates or by side ditches in two rows and two oscillating plates.

CONSTITUTION: When an oscillator 4 is actuated, horizontal actions are repeatedly given through an oscillating beam 3 to oscillating plates 2, the oscillating plates 2 undergo a vibrating displacement at a pin connecting portion 6 as the supporting point under the ground, and the ground A to be judged undergoes a shear deformation. Also, the void water pressure among soil and sand goes up abruptly, excessive void water pressures are generated, and the ground A is liquefied. In this case, the variations in the aimplitude and frequency of vibration given are read out by a void water pressure guage 16 and a seismometer (accelero meter) 17 buried under the ground A and the rise and variations of void water pressures as well as excessive void water pressures are also read out likewise. By this, the occurrence and degree of the liquefying of the ground A can be judged.