PROBLEM TO BE SOLVED: To provide an expansion joint structure which can effectively absorb displacement caused between a ceiling material 2 and a wall during earthquakes, which has consistency provided in a shape between a joint material and a ceiling frame and a shape between the joint material and the ceiling material 2, and which is excellent in designability of an internal appearance.SOLUTION: A dovetail groove 12 is formed in each of inside surfaces of first and second edges 10 and 11 of a cover material 3 formed in an L-shaped cross-section; uneven streaks 13 are provided on each of outside surfaces of the first and second edges 10 and 11; and the first or second edge 10 or 11 of the cover material 3 is fixed to a wall material 1. A gap is provided between an end of a ceiling material 2 and the wall material 1, and the end of the ceiling material 2 of a ceiling backing material employing an earthquake resistant structure is supported by abutting on the first or second horizontally-provided edge 10 or 11 of the cover material 3.