To provide a horizontal joint mortar laying form allowing joint mortar between concrete blocks for configuring a block fence or the like to be uniformly laid without taking labor and time.

A horizontal joint mortar laying form 10 allows horizontal joint mortar A to be laid on top faces of concrete blocks C for configuring a block masonry body B by filling the inside of the concrete form with the horizontal joint mortar A. In the horizontal joint mortar laying form 10, closing plates 12 for respectively closing caves O formed in the concrete blocks C are disposed in a rectangular form body 11, and a space part in the form body 11 other than the closing plates 12 is defined as a filling space K which is filled with the horizontal joint mortar A.