To provide a connectable concrete block capable of being stably laid down on a road by fitting adjacent blocks to each other even if the road has unevenness, slope, twist, curve, or the like.

Concrete blocks 100 are disposed so that the side surfaces face each other and constitute a compartment or a boundary. The concrete block 100 includes a projection 10 which is formed on one side-surface 70 and the front end of which is formed in a generally semi-spherical convex shape, and a generally semi-spherical concave recess 20 which is formed in the other side-surface 80 on the opposite side of the one side-surface 70. The distance between the one side-surface 70 and the highest part of the projection 10 is longer than the distance between the other side-surface 80 and the deepest part of the recess 20.