Abstract: Provided are cone penetrometers for measuring the impedance of the ground. In an embodiment, the cone penetrometer comprises an inner electrode, an outer electrode, an insulator layer and a penetrating rod. The inner electrode includes a cone, a first contact portion to which terminal cables of an impedance meter are connected, and a metal rod. The metal rod has a diameter smaller than that of the cone. The metal rod has a front end connected to the bottom of the cone and a rear end connected to the first contact portion. The outer electrode has an inner diameter smaller than the diameter of the cone and is in the form of a hollow tube accommodating the metal rod. The insulator layer is formed between the inner electrode and the outer electrode to prevent short circuits between the two electrodes. The penetrating rod is in the form of a hollow tube accommodating the outer electrode. The use of the cone penetrometers improves the accuracy and reliability of the measured results.