PURPOSE: To quickly determine the quality of soil by a method in which a rod having a sound sensor on its tip is penetrated into the ground and the wave form of the sound is compared with standard wave form for each soil quality being classified in advance.

CONSTITUTION: A sound sensor 2 is attached to a rod 5 having a cone 1 on its tip. A soil-crushing sound generated when driving the rod 5 into the ground is sent to a receiver set on the ground's surface by wire or wireless telecommunication for recording. The wave form so recorded is compared with a standard wave form for each soil quality being classified in advance to determine the quality of soil. The soil quality can thus be surveyed at the same time as the rod 5 is continuously driven for penetration testing, whereby the operating time can be shortened.