To prevent the mixing of an error into a measurred value by the slipping of a screw point in a method and a device for investigating soil, in which a static penetration resistance is obtained.

A drill 8 is added to a penetration front-end tool, the screw point is exchanged with the drill and soil is excavated and the state of the stop of the penetration is released when the penetration of the screw point is stopped or brought to the state close to the stop even when the rod is rotated by using the method and the device for investigating soil, in which the screw point 4 is attached at the lower end of the rod 3, a weight 6 is placed to the upper section of the rod, the rod is erected vertically on a ground surface and the weights are increased, the screw point is penetrated into a ground and the rod is rotated when the weights reach a required loading. In the method and the device for investigating soil, after no required layer is confirmed, the drill is returned to the screw point and the penetration is continued and an operation is repeated until the required layer is obtained.