To render the strength of concrete retainable without destroying natural environments by furnishing decoration means in which a part of lumber is buried by controlling its exposure degree on the surface an arbitrarily- configured concrete block.

Lumber 2 is arranged to be fixed at the side surface 1a of a concrete block 1 in a manner that its lower end part 2b is set at the lower end surface of the side surface 1a, and its upper end surface 2a is slightly projected from the upper end surface of the side surface 1a allowing a part of the peripheral surface 2c of lumber 2 to be exposed therefrom. For example, lumber 2 is fastened by sticking joint levers on a contact surface between the peripheral surface 2c of lumber and the concrete block 1, or fastened to the concrete block by the use of branches of lumber 2. Its execution is carried out for retaining by increasing and decreasing the concrete block 1 having lumber 2 arranged to be disposed in accordance with the height of an embankment or a quay. Since an exposure degree of concrete is minimized by lumber 2, the strength of concrete blocks is made retainable without destroying natural environments.