PURPOSE: To obtain a breakwater which can be made wide at the upper face thereof and which is excellent in a beauty point without much increase of cost.

CONSTITUTION: A top cover 3 having a wider breadth than the upper face of a caisson 1 and a nearly U-shaped section is placed on the caisson 1 disposed opposite to waves 2 to cover the upper face and the front and rear faces of the upper part with the cover 3. The underface of both front and rear ends of the top cover 3 is made to form a wave profile for instance. A plurality of these caissons 1 and the top covers 3 are arranged to form a breakwater. In this way, the width, of the upper face of breakwater can be widened with the minimum cost up while using a caisson 1 with almost the same width with conventional ones. Since the front edge 3b or the rear edge 3c of the top cover 3 with wave profiles project in the three-dimensional directions back and forth from the front wall face 1b or the rear wall face 1c of the caisson 1, the breakwater is excellent in the beauty point as well.