A concrete block having comparatively light weight and capable of being manufactured easily and used in various fields of application; a block joint for the concrete blocks, capable of carrying out the arrangement of the concrete blocks simply and retaining the arranged concrete blocks in good order; and a structure made by using the concrete blocks and the block joints. The joint (1,2) has seats (1b,2b) which are formed by cutting off predetermined portions thereof and adapted to restrict positions in which the concrete blocks (3) are arranged horizontally and vertically so that horizontally adjacent and vertically adjacent concrete blocks have clearances therebetween, and which support corner portions of the concrete blocks (3) thereon, each of the concrete blocks (10) being formed in a cubic or parallelepipedal outer shape so that it has an outwardly opened hollow structure, by using a split core (12) which can be broken down and removed after the concrete has been hardened, thus obtaining a structure of which the interior of the concrete blocks (10) communicate with each other when a plurality of blocks (10) are horizontally and vertically arranged.