To provide a penetration rod for use in a penetration test for determining soil properties on the basis of rotational load torque acting on a screw point, which can detect the rotational load torque acting on the screw point alone, by eliminating an influence exerted by skin friction of the rod.

The rod 2 and the screw point 3 are connected together via a unidirectional coupling mechanism 4; and the unidirectional coupling mechanism 4 makes the rod 2 and the screw point 3 integrally rotatable during normal rotation, and makes only the rod 2 rotatable during reverse rotation.