PURPOSE: To measure penetration depth of a pile or the like into the ground by measuring eight of a flexible chain having a uniform eight and connected to a hammer device.

CONSTITUTION: A container 19 for a chain 18 and a weight sensor 20 are installed on a lower part of a leader 12. One end of the chain 18, having a uniform weight and contained in the container 19, is connected to a wire 14 of a hammer device 11 via a connecting device 17. The hammer device 11 is moved downward, while drawing the chain 18 from the container 19, the weight of the chain that remains the container 19 is measured by the eight sensor 20 at the moment, when the hammer strikes a pile 13 and a signal is transmitted to a data logger/processor 21 via radio communication devices 23a, 23b. The difference between the total weight of the chain 18 and the weight of the drawn out chain is calculated to determine the penetration depth of the pile 13.