Disclosed herein is a non-slip reinforcing bar coupler including: a body which has a body part of a pipe shape, a protrusion part formed in the middle of the body part, a pair of first screw threads formed on the outer surface of the body part and at both sides of the protrusion part, a pair of insertion holes formed at both sides of the body part, and a stopper formed in the middle of the inside of the body part; and a cap which has a cap insertion hole formed at one side, a cap body formed on the inner surface of the other side and having a second screw thread screw-coupled with the first screw thread, and a second inner sloping side formed on the inner surface of the cap insertion hole.