The present invention is a steam turbine rotor blade assembly including: an airfoil; a shroud provided at a tip of the airfoil; a blade root (dovetail) projecting toward a radially internal circumferential side of a turbine rotor and fitted to a root attachment provided on an outer circumferential portion of the turbine rotor; a platform provided between the airfoil and the blade root; a pin provided between the blade root and the root attachment; a bore formed between respective surfaces of the shrouds facing each other and included in the respective adjacent rotor blades; and a bar-like member provided in the bore.