To solve the problem that it has been difficult to normally bring connecting faces of concrete blocks into contact (overall contact) with each other between the existing side and the connecting side in the case of very heavy concrete blocks.

Female screws 14 and 15 are formed with a prescribed difference H in height at locations each close to front and rear connecting faces on side surfaces of a concrete block. Bolt insertion holes 31 and 32 are formed in a connecting plate 3 at the same interval from each other as the linear distance between two female screws when connecting faces 11 and 12 of two concrete blocks are connected to each other. The connecting plate 3 and bolts 4 and 5 each to be helically engaged with the female screws are used to bring a connecting face of a connecting-side concrete block 1B on the low-position female screw side close to a connecting face of an existing-side concrete block 1A and temporarily connect the female screw on each side with the connecting plate. After the connecting-side concrete block is lowered to the ground, by tightly fastening both bolts, both concrete blocks are easily and beautifully connected to each other.

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