To provide a horizontal joint material capable of restraining a compressive displacement quantity in the depth direction, when the horizontal joint material is compressed by a load of an upper side panel wall.

This rubber horizontal joint material 1 is interposed in a joint space part 10 between vertically adjacent panel walls 1 among a large number of panel walls 1 for constructing a concrete retaining wall. A joint body 12 forming a main body part of the horizontal joint material 11, is formed by molding and vulcanizing a joint material of kneading an unvulcanized rubber material and a fiber material in a band plate shape corresponding to the joint space part 10, and has rubber elasticity. The fiber material is internally arranged over the whole area in the thickness direction, the longitudinal direction and the depth direction. A recessed part 13 for restraining the compressive displacement quantity in the depth direction when the joint body 12 is compressed by the load of the upper side panel wall 1, is formed on at least one side surface among both upper-lower surfaces of the joint body 12.