This study deals with the 2D scour at the trunk section of a rubble-mound breakwater. Two breakwater models with slopes of 1:1.2 and 1:1.75 are employed for the experimental study of the scour in a wave flume. 2D scour at a vertical-wall breakwater was also included as a reference case. Tests were conducted with both regular waves and irregular waves. It was found that the scour/deposition pattern in front of the rubble-mound breakwater emerges in the form of alternating scour and deposition areas lying parallel to the breakwater, similar to the case of the vertical-wall breakwater. The maximum scour depth, however, was found to be smaller in the present case than that of the vertical-wall breakwater case. In the case of the irregular waves, the scour depth at the breakwater decreases with respect to that experienced in the case of the regular waves. Countermeasures for toe protection were also investigated for the following cases: (1) the protection apron with one layer of stones and (2) that with several layers of stones. The mechanism of slumping down of stones of the protection apron was also considered. The results of the toe protection study are given in the form of diagrams.