The invention relates to a rock anchor bolt. In the rock anchor bolt, a centering member includes an outlet hole for removing any leakage water flowing into a borehole. The rock anchor bolt includes asealing device provided around the outer end of a tube to seal the borehole watertight as a tightening nut is being tightened, and an outlet tube provided in a casting space between the tube and a drawbar to carry out the leakage water as grouting paste is being injected, the inner end of which outlet tube extends to the vicinity of an expansion member and the outer end of the outlet tube extendsout from the outlet hole of the centering member. The tube has one or more first casting holes at the outer end of the tube in the vicinity of the sealing device and one or more second casting holesat the inner end of the tube in the vicinity of the expansion member. As grouting paste is being injected, it fills the casting space between the tube and the drawbar as well as the space between theborehole and the tube from the outer end toward the inner end so as to force any leakage water ahead of the grouting paste to the inner end of the outlet tube.